This trial is part of the Physicians Health Study, sponsored by the National Heart, Lung, and Blood Institute (NHLBI) of the National Institutes of Health, with funding for eye epidemiologic data evaluations provided by the NEI. It is an ongoing, randomized, placebo-controlled trial of aspirin in the prevention of cardiovascular mortality and of beta-carotene in the prevention of cancer. Following randomization, each of the 22,071 physicians enrolled was assigned to one of four groups to take either aspirin or its placebo and beta-carotene or its placebo. Followup questionnaires are sent 6 and 12 months after randomization and every 12 months thereafter. The average length of followup is now greater than 12 years.