A prospective study of 1969 patients with intermittent claudication receiving placebo medication for a minimum of 1 year is reported. Patients were carefully monitored and only four patients were lost to follow-up. Annual mortality was 4.3%. Thirty-six patients developed a definite myocardial infarction, 27 a major stroke, 32 required a major amputation and 111 required surgical or radiological intervention for deteriorating ischaemia of the leg. The entry characteristics of the patients were analysed as a predictor of serious cardiovascular events. The most sensitive predictors of total mortality were age, history of coronary heart disease and an ankle/arm pressure ratio below 0.5. Of the laboratory measurements performed only the initial white cell count was a significant predictor of myocardial infarction, stroke and vascular deaths.