We assessed the efficacy of adding nifedipine to the conventional treatment of unstable angina in 138 patients in a prospective, double-blind, randomized, placebo-controlled trial. There was no difference between the two groups in the dose of conventional antianginal medication or in age, prior myocardial infarction, ejection fraction, or other risk factors. Failure of medical treatment (defined as sudden death, myocardial infarction, or bypass surgery within four months) occurred in 43 of 70 patients given placebo and in 30 of 68 given nifedipine. Kaplan-Meier survival-curve analysis of the number and time dependence of treatment failures demonstrated a benefit of nifedipine over placebo (P = 0.03). The benefit was particularly marked in patients with ST-segment elevation during angina (P = 0.02). Side effects (transient hypotension or diarrhea) required withdrawal of the drug from four patients given nifedipine and from one given placebo. We conclude that the addition of nifedipine to conventional therapy is safe and effective in unstable angina.