Dissenting Opinion by
Judge Mencer:I respectfully dissent.
The burden is on a claimant to establish by substantial evidence that the disability has “increased after the date of the prior award.” Harry Halloran Construction Co. v. Workmen’s Compensation Appeal *79Board, 39 Pa. Commonwealth Ct. 272, 274, 395 A.2d 325, 326 (1978) (emphasis omitted). This proof must he made “by precise and credible evidence which [is] of a more definite and specific nature than that upon which initial compensation is based." Pittsburgh Des Moines Steel Co. v. Workmen’s Compensation Appeal Board, 31 Pa. Commonwealth Ct. 530, 534, 377 A.2d 833, 835 (1977). A modification proceeding cannot be used to relitigate the percentage of disability determined in a prior award. Workmen’s Compensation Appeal Board v. Booth & Flinn Co., 18 Pa. Commonwealth Ct. 369, 336 A.2d 448 (1975).
Here, claimant’s sole medical witness, who had examined claimant both in 1967 and in 1975, did testify that claimant was unable to perform his prior carpentry job but failed to state whether, in his opinion, claimant’s disability had increased after the date of the prior partial disability determination. Moreover, this witness admitted that claimant could perform light carpentry work. Although claimant testified that his pain had been increased each year after his injury, nevertheless, in view of claimant’s other non-work-related diseases affecting his left leg (phlebitis and Paget’s disease), I do not believe that claimant’s lay testimony is sufficient to establish that his 1966 injury has caused the increased pain or its concomitant disabling effect. Under these circumstances, I must conclude that claimant’s failure to produce medical testimony establishing a change from partial to total disability is fatal to claimant’s position. Klingler v. Workmen’s Compensation Appeal Board, 50 Pa. Commonwealth Ct. 335, 413 A.2d 432 (1980). See also Morgan v. Giant Markets, Inc., 483 Pa. 421, 397 A.2d 415 (1979).
Accordingly, I would reverse the Workmen’s Compensation Appeal Board’s grant of total disability benefits to William Brown.
*80Judges Williams and Palladino join in this dissent.