The National Registry of Drug-Induced Ocular Side Effects has accumulated 30 cases of suspected allopurinol-induced lens changes. The cataracts associated with this antihyperuricemic agent are initially anterior and posterior lens capsule changes with anterior subcapsular vacuoles. With time, wedge-shaped anterior and posterior cortical haze occurs, along with dense posterior subcapsular cataracts. Histologic studies of these cataracts showed no unique or identifying features. These cases do not prove a cause-and-effect relationship, but raise the suspicion that allopurinol may be cataractogenic in some patients. Additional case reports and lens material should be sent to the National Registry of Drug-Induced Ocular Side Effects, Oregon Health Sciences University, 3181 S.W. Sam Jackson Park Rd., Portland, OR 97201.