The effect of selenium supplementation was evaluated in 81 patients with acute myocardial infarction in a double-blind, placebo-controlled study. Patients were randomised into two treatment groups receiving either selenium-rich yeast (100 micrograms/day) or placebo in addition to conventional drug therapy for a 6-month period. During treatment the mean serum selenium concentration increased from 82 micrograms/l to 122 micrograms/l (p less than 0.001) in the selenium supplemented group and remained unaltered in the placebo group (83 micrograms/l). During the 6-month follow-up period there were 4 cardiac deaths in the placebo group whereas no patients in the selenium group died during the follow-up period. Furthermore, there were 2 nonfatal reinfarctions in the placebo group and one nonfatal reinfarction in the selenium group. The results encourage further studies to evaluate the efficacy of antioxidants in the prevention and therapy of acute myocardial infarction.