Male patients were given long-term treatment with probucol, and the effects of the drug were compared with those of placebo. Probucol lowered plasma cholesterol levels, and this action was sustained with time; it had no significant effect on triglycerides. The only adverse reaction of some clinical import was bouts diarrhea, which did not usually require withdrawal of the drug. In view of these results and of the death figures during the observation period, the authors envisage to undertake a larger scale study of secondary prevention of mortality in patients with coronary disease treated with probucol.