We report the results of a randomized double-blind, multicenter trial comparing sulfinpyrazone (200 mg four times a day) and a placebo in the prevention of cardiac mortality among 1558 patients followed for an average of 16 months, beginning 25 to 35 days after a documented myocardial infarction. All but one of the 106 deaths in the group were cardiac; 59 were sudden. The reduction in cardiac mortality at 24 months in the sulfinpyrazone group was 32 per cent (P = 0.058), and the reduction in sudden death was 43 per cent (P = 0.041). The benefit of sulfinpyrazone was attributable entirely to a reduction in sudden death during the second through seventh months after infarction, when there were 35 cardiac deaths in the placebo group and 17 in the sulfinpyrazone group (P = 0.021); of these deaths, 24 in the placebo group and six in the sulfinpyrazone group were sudden cardiac deaths -- a sulfinpyrazone-induced 74 per cent reduction in the calculated mortality rate (P = 0.003). We conclude that sulfinpyrazone prevents sudden cardiac death during the high-risk period shortly after an acute myocardial infarction, but that there is no further apparent effect beyond the seventh month after infarction.