delivered the Opinion of the Court.
The United States Court of Appeals for the Tenth Circuit, pursuant to C.A.R. 21.1, certified the following question of law:
Does discovery of an initial asbestos-related disease (in this case asbestosis-related pleural disease manifested by pleural thickening and pleural calcification) trigger the running of a statute of limitations on a separate, distinct, and later-manifested disease (here asbestosis) engendered by the same asbestos exposure? 1
We agreed to answer the question and we conclude the answer is no.
I
On June 9, 1987, plaintiff Raymond Miller filed a complaint for damages alleging that, as a proximate result of his exposure to the defendants’ defective and unreasonably dangerous asbestos products, he had developed asbestosis, an asbestos-related disease.2 The complaint also sought damages for increased risk of contracting lung cancer, pleural mesothelioma, peritoneal mesothelioma, laryngeal carcinoma, cancer of the alimentary canal and digestive tract, and cancer of the kidney caused by the inhalation and ingestion of asbestos dust and fibers.
The defendants moved for summary judgment pursuant to Fed.R.Civ.P. 56, contending that Miller was advised of a diagnosis of asbestosis in October 1981, October 1983, and April 1984, see Miller v. Celotex Corp., 708 F.Supp. 306, 308-09 (D.Colo.1989), and that the statute of limitations bars prosecution of his claim for relief as a matter of law.3 Miller responded that although he was diagnosed with *113benign pleural thickening and pleural calcification prior to 1983, he was not diagnosed as having asbestosis until 1985. Based on Miller’s medical records and testimony contained in depositions and affidavits, the United States district court entered summary judgment for the defendants, finding that Miller knew or reasonably should have known facts essential to his claim against the defendants in September 1981, and no later than April 1984. Id. at 310. The district court did not address whether the “manifestation of a plaintiff’s benign asbestos related condition triggers the running of the statute of limitations on any later manifested malignant asbestos related disease engendered by the same asbestos exposure.” Id.
II
In Colorado, the discovery rule provides that a “cause of action for injury to [a] person ... shall be considered to accrue on the date both the injury and its cause are known or should have been known by the exercise of reasonable diligence.” § 13-80-108(1), 6A C.R.S. (1987). A claim for relief “does not accrue until the plaintiff knows, or should know, in the exercise of reasonable diligence, all material facts essential to show the elements of that cause of action.” City of Aurora v. Bechtel Corp., 599 F.2d 382, 389 (10th Cir. 1979) (applying Colorado law). The statute of limitations does not begin to run at the mere discovery of a physical process leading to an injury. Financial Assoc, v. G.E. Johnson Const. Co., 723 P.2d 135, 138 (Colo.1986) (applying the discovery rule to improvement of real property). An exception exists, however, if the discovery is of a defect causing the injury, id.; but such is not the case here.
The appeal to the Tenth Circuit is from an order granting summary judgment. The relationship of pleural thickening and pleural calcification to asbestosis is a question of fact. In certifying the question of law, the Tenth Circuit stated:
We recognize that the relationship between asbestos-related pleural disease and asbestosis is a factual question. Because this is an appeal from a summary judgment and there is conflicting evidence in the record, it must be assumed that asbestosis is separate and distinct from and not a complication of asbestos-related pleural disease. We thus respectfully request the Colorado Supreme Court to focus on the narrow legal issue of whether a statute of limitations begins to run anew for a separate, distinct, and later-manifested disease caused by exposure to asbestos. The number of asbestos-related disease cases pending in the United States District Court for the District of Colorado is substantial, and a decision by the Colorado Supreme Court on our certified question is expected to govern the ultimate disposition of a considerable portion of those cases.
Certification of Question of State Law from the United States Court of Appeals for the Tenth Circuit at 2-3. Accordingly, we assume, as the question does, that asbestosis is a separate and distinct disease.
Based on the statement of the certified question, knowledge of the existence of benign pleural thickening and pleural calcification does not constitute proof of the material facts or injury necessary to maintain a personal injury claim for asbestosis. The discovery of benign pleural thickening and pleural calcification does not trigger the running of the statute of limitations and may not be substituted for subsequent knowledge of the existence of a claim for asbestosis.
Accordingly, we answer the certified question in the negative.
VOLLACK, J., dissents, and ROVIRA, C.J., joins in the dissent.. The factual and procedural background is set forth in the district court opinion. Miller v. Celotex Corp., 708 F.Supp. 306 (D.Colo.1989). The narrow issue in this case has not been addressed by this court. We have been advised by the Tenth Circuit of the decisions reached in other jurisdictions. See Joyce v. A.C. & S., Inc., 785 F.2d 1200, 1203-15 (4th Cir.1986) (applying Virginia law); Ross v. Johns-Manville Corp., 766 F.2d 823, 826 (3d Cir.1985) (applying Pennsylvania law); Wilson v. Johns-Manville Sales Corp., 684 F.2d 111, 117-21 (D.C.Cir.1982); Pearson v. Johns-Manville Sales Corp., 525 F.Supp. 671, 674 (D.D.C.1981); Eagle-Picker Indus., Inc. v. Cox, 481 So.2d 517, 520 (Fla.Dist.Ct.App.1985), review denied, 492 So.2d 1331 (Fla.1986); VaSalle v. Celotex Corp., 161 Ill.App.3d 808, 813-14, 113 Ill.Dec. 699, 702-03, 515 N.E.2d 684, 687-88 (1987); Smith v. Bethlehem Steel Corp., 303 Md. 213, 233, 492 A.2d 1286, 1296 (1985); Larson v. Johns-Manville Sales Corp., 427 Mich. 301, 315-19, 399 N.W.2d 1, 7-9 (1986); Fusaro v. Porter-Hayden Co., 145 Misc.2d 911,-, 548 N.Y.S.2d 856, 859-60 (Sup.Ct.1989). We answer the question based upon our interpretation of Colorado law and do not rely upon the cases cited for our decision.
. Affidavits by experts, which were submitted in opposition to the motion for summary judgment, set forth that asbestosis is a fibrosis (scarring) of the parenchyma (the substance of the lung). Because scarred lung tissue cannot pass oxygen into, or carbon dioxide out of, the blood, asbestosis can cause impaired breathing ability. Severe asbestosis may result in death.
Pleural thickening refers to the thickening of the visceral pleura (the thin transparent tissue surrounding the lung) and the parietal pleura (similar tissue lining the chest wall). The pleura is not a part of the structure of the lung, but rather provides an airtight capsule around the lung and a smooth surface for the lung to move against. Pleural calcification is manifested by pleural plaques, which are circumscribed areas of pleural thickening containing calcium. Pleural thickening and pleural calcification do not cause pain or impair breathing.
.The defendants assert that Miller’s claim for relief was barred under Colorado’s two-year statute of limitations governing actions brought against a manufacturer. § 13-80-127.5(1), 6A C.R.S. (1977). Prior to 1986, section 13-80-127.5(1) provided:
Notwithstanding any other statutory provisions to the contrary, all actions except those governed by section 4-2-725, C.R.S.1973, brought against a manufacturer or seller of a' product, regardless of the substantive legal theory or theories upon which the action is brought, for or on account of personal injury, death, or property damage caused by or resulting from the manufacture, construction, design, formula, installation, preparation, assembly, testing, packaging, labeling, or sale of any product, or the failure to warn or protect against a danger or hazard in the use, misuse, or unintended use of any product, or the failure to provide proper instructions for the use of any product shall be brought within two years after the claim for relief arises and not thereafter.
Section 13-80-127.5(1) was repealed in 1986 and sections 13-80-106 and 107, 6A C.R.S. (1987), now govern limitations of actions against manufacturers of products and manufacturing equipment.