We conducted a two-part study to determine whether any positive association between the use of allopurinol and the development of cataracts could be demonstrated. Study 1 included 251 Boston-area patients hospitalized for cataract and 753 matched controls. Two cataract patients were regular allopurinol users as compared with six control patients. The relative risk for cataract comparing allopurinol users with nonusers was 1.0 (95% exact confidence interval 0.14, 4.7). Study 2 included 389 patients from the Puget Sound, Washington, area who were hospitalized for cataract surgery during a five-year period (551,543 person-years). The rate of hospitalization for cataract in patients 30 to 49 years old was 0/992 person-years for allopurinol users and 78/366,960 (2.1 per 10(4)) person-years for nonusers. The rate of hospitalization for cataract in patients 50 to 64 years old was 3/2,270 (13.2 per 10(4)) person-years for allopurinol users and 308/184,583 (16.7 per 10(4)) person-years for nonusers.