Appellant contends the trial court erred in admitting expert testimony as to the mere possibility of a causal connection between the chemical exposure and appellee’s terminal cancer. We agree.
Dr. Kravitz, a medical expert for appellee, testified that “with a reasonable degree of probability, it is likely that this combination of those three chemicals could have caused the cancer.” (Emphasis added.)
It is well-settled that the establishment of proximate cause through medical expert testimony must be by probability. At a minimum, the trier of fact must be provided with evidence that the injury was more likely than not caused by defendant’s negligence. See Cooper v. Sisters of Charity (1971), 27 Ohio St. 2d 242, 252 [56 O.O.2d 146], Opinions expressed with a lesser degree of certainty must be excluded as speculative.3
The evidence seeking to causally connect appellee’s pancreatic cancer to his exposure to Liquid Envelope Blue was merely speculative and conjectural, and did not rise to the requisite standard of probability. See Brandt v. Mansfield Rapid Transit, Inc. (1950), 153 Ohio St. 429 [41 O.O. 428]. Dr. Rudolph specifically stated that he could not causally relate the pancreatic cancer to the exposure with a reasonable degree of phar-macologic certainty. Although Dr. Kravitz did state that he was testifying to a “reasonable degree of probability,” he modified his statement by the word “could.” Thus, he was not testifying that the cancer was causally linked to the exposure, but only that such a causal connection could, but *370not necessarily did, exist. Therefore, this portion of Dr. Kravitz’s testimony should not have been admitted into the record over appellant’s objections. The trial court erred to the prejudice of appellant in allowing the jury to consider this testimony.
Appellant further contends the trial court abused its discretion in allowing appellee to introduce the foregoing expert testimony over repeated objections purporting to establish a causal connection between the pancreatic cancer and the chemical exposure because no pretrial notice had been given regarding this claim. This contention possesses merit. While the admissibility of evidence is a matter generally within the sound discretion of the trial court, the trial court does not have unbridled discretion in this regard. See Schaffier v. Ward (1985), 17 Ohio St. 3d 79, 80; Calderon v. Sharkey (1982), 70 Ohio St. 2d 218 [24 O.O.3d 322].
“One of the purposes of the Rules of Civil Procedure is to eliminate surprise. This is accomplished by way of a discovery procedure which mandates a free flow of accessible information between the parties upon request, and which imposes sanctions for failure to timely respond to reasonable inquiries.* * *” Jones v. Murphy (1984), 12 Ohio St. 3d 84, 86.
Civ. R. 26(E)(1) provides that “* * * [a] party is under a duty seasonably to supplement his response with respect to any question directly addressed to * * * (b) the identity of each person expected to be called as an expert witness at trial and the subject matter on which he is expected to testify.” An objective of this rule is to provide opposing counsel with updated and complete discovery regarding the substance of expert testimony. This duty to supplement responses on the subject matter of expert testimony is necessary because preparation for effective cross-examination is especially compelling where expert testimony is to be introduced. See Smith v. Ford Motor Co. (C.A. 10, 1980), 626 F. 2d 784; Scott & Fetzer Co. v. Dile (C.A. 9, 1981), 643 F. 2d 670.
The interrogatories propounded to appellee included a request to “[i]dentify all persons who [sic] you expect to call as expert witnesses at trial, including a summary of the testimony that each such witness is expected to give.” Appellee listed Dr. Kravitz as a witness in a supplemental response to this interrogatory, but failed to further supplement his response to include Dr. Kravitz’s testimony about the potential causal link between appellee’s exposure and his cancer. This failure to properly supplement this response violated Civ. R. 26(E)(1). While appellant knew that appellee had pancreatic cancer, appellant was unaware there would be a claim that the chemical exposure caused the cancer.
Expert testimony may be excluded as a sanction for the violation of Civ. R. 26(E)(1)(b). See Jones v. Murphy, supra, at 86; Huffman v. Hair Surgeon, Inc. (1985), 19 Ohio St. 3d 83. In Shelak v. White Motor Co. (C.A. 5, 1978), 581 F. 2d 1155, 1159, a case involving surprise which had almost identical facts as the case at bar, the court found that the trial court committed an abuse of discretion by allowing a medical expert to testify about *371a previously undisclosed causal connection between an injury and a subsequent medical problem, stating:
“The failure of the plaintiff candidly to reveal his claim of injury * * * goes to the question of damages. Plaintiffs disregard for the federal rules of discovery in this area created a ‘trial by ambush’ which those rules are designed to prevent.* * * [I]f discovery has any purpose, plaintiff’s opponent was entitled, upon the unveiling of the * * * contention, to a reasonable opportunity to prepare to defend against it.”
Similarly in Scott & Fetzer Co. v. Dile, supra, at 673-674, the court held that it was an abuse of discretion to allow a party to introduce testimony by previously undisclosed witnesses and to use a new theory of the case.
There appears to be an element of “ambush” in the present case. Ap-pellee never disclosed that he was asserting the cancer claim prior to trial and, in fact, during the argument on the motion in limine immediately preceding the trial, indicated he did not know what the experts would say on that subject. Therefore, appellant had no discovery on this purported causal connection in spite of diligent efforts toward this end.
The trial court’s error with respect to the surprise was compounded by its submission to the jury of the actual expert testimony which did not rise to the requisite standard of opinion testimony. This error was prejudicial since it allowed the jury to consider inadmissible evidence on a highly inflammatory subject — terminal pancreatic cancer.
For these reasons the court of appeals’ decision is reversed and the cause is remanded for a new trial.
Judgment reversed and cause remanded.
Holmes and Wright, JJ., concur. Locher and Douglas, JJ., concur in judgment only. Celebrezze, C.J., Sweeney and C. Brown, JJ., dissent.“Proof of possibility is not sufficient to establish a fact; probability is necessary. * * *” Drew v. Indus. Comm. (1940), 136 Ohio St. 499, 501 [17 O.O. 113]; see, also, Kuhn v. Banker (1938), 133 Ohio St. 304, 312 [10 O.O. 373]. “Probable is more than 50% of actual.* * *” Cooper, supra, at 253. Evidence which only shows that a condition could have been the result of an injury is “insufficient proof to warrant submission of the cause to the jury.* * *” Drew v. Indus. Comm., supra, syllabus. See, also, Drakulich v. Indus. Comm. (1940), 137 Ohio St. 82 [17 O.O. 398]; Brandt v. Mansfield Rapid Transit, Inc. (1950), 153 Ohio St. 429 [41 O.O. 428]; Gedra v. Dallmer Co. (1950), 153 Ohio St. 258 [41 O.O. 274].