The effect of an aldose reductase inhibitor, CT-112 (5-(3-ethoxy-4-pentyloxyphenyl)2,4-thiazolidinedione), ophthalmic solution on wound healing in the corneal epithelium of rats fed on 50% galactose diet was investigated in correlation with CT-112 concentration. Rats were divided into 6 groups and those in 5 groups were fed on 50% galactose diet and 10 microliter of 0.1, 0.25, 0.5 and 1% CT-112 ophthalmic solutions or of their vehicle were instilled into both eyes 4 times a day. The animals in the remaining one group were fed on the regular diet and no treatment was given. After 18 days, the whole corneal epithelium was scraped off and the rate of reepithelialization was investigated over a 4-day period. Reepithelialization was delayed in galactosemic rats, but the instillation of CT-112 ophthalmic solutions improved the wound healing, although no differences in efficacy was found at the concentrations used. Moreover, the appearances of the cornea at 4 days after epithelial scraping were improved dose-dependently by the instillation of CT-112.