The crystalline lenses of hypercholesterolemic patients were assessed before and after 48 weeks of treatment with lovastatin or placebo to determine the effect of lovastatin on the human lens. Patients were given a biomicroscopic (slit-lamp) examination of the lens, and a previously validated, standardized classification system was used to describe the findings. A total of 8,245 patients were randomly assigned in equal numbers to treatment with placebo or lovastatin 20 or 40 mg once or twice daily in this double-blind, parallel-group study. Statistical analyses of the distribution of cortical, nuclear and subcapsular opacities at 48 weeks, adjusted for age and presence of an opacity at baseline, showed no significant differences (p less than 0.01) between the placebo and lovastatin-treated groups. Visual acuity assessments at week 48 were also not found to have significantly different distributions among treatment groups. Moreover, no significant differences were found among the groups in the frequencies of greater than or equal to 2-line worsening in visual acuity with concurrent progression in lenticular opacity, cataract extraction, or any spontaneously reported adverse ophthalmologic experience. No evidence was found for an effect of lovastatin on the human lens after 48 weeks of treatment.