To evaluate the role of prepared cysteine per os in corneal epithelial healing in transgenic mice (B6(A)-Rpe65rd12/J) after excimer laser photoablation. In our prospective case series, 60 eyes of 30 mice had uneventful bilateral excimer laser photoablation. A first group, composed of 15 mice, received standard topical post-operative therapy with tobramycin, diclofenac and dexamethasone eyedrops, plus cysteine 5 mg 5 microg/10 microl phosphate-buffered saline (3 times a day for 1 week) per os or until corneal re-epithelialization was complete. The control group of 15 mice received standard post-operative therapy plus placebos. The mice were monitored daily, commencing the day after surgery, for 7 days to evaluate the corneal re-epithelialization rate using a video slit-lamp camera with a cobalt blue light. The mean diameters of corneal wounds were measured. Videotaped images were recorded and analysed by computer planimetry. All the eyes of the mice treated with cysteine healed completely by day 5 after surgery, with a mean re-epithelialization time of 92 +/- 10 h (SD); the mean re-epithelialization time was 125 +/- 8 h in eyes that received the placebo. There were no statistically significant differences between the 2 groups in corneal haze presentation during follow-up, perhaps because the time period was too brief (7 days). However, corneal clarity in the study group was greater than in the control group, as shown on slit-lamp biomicroscopy. No side effects or toxic effects were documented. These data suggest that cysteine significantly accelerates epithelial healing after excimer photoablation. A further clinical study should be performed to confirm the results obtained in this study, and the long-term efficacy of cysteine in preventing corneal haze.