We treated three patients who had intraepithelial neoplasia involving the visual axis and a subsequent decrease of visual acuity with topical mitomycin C 0.02% four times daily for ten to 22 days. In two of the three cases, the intraepithelial neoplasia was histologically confirmed. The intraepithelial neoplastic lesion was replaced by biomicroscopically normal epithelium within nine weeks of the beginning of drug administration and did not recur during the four to 12 months of follow-up. Adverse reactions to topical mitomycin in two patients ranged from minimal conjunctival hyperemia after 14 days to marked hyperemia, ocular pain, and blepharospasm after 22 days. These signs and the symptoms, however, disappeared after the drug was discontinued. Administration of topical mitomycin C 0.02% for two weeks may be an effective treatment for corneal intraepithelial neoplasia that affects the visual axis.