One hundred and two patients participated in a 4 week programme of intensive exercise training early after myocardial infarction. Lipid levels were measured before and after exercise training. The mean exercise capacity increased by 49% (P = 0.0001). Twenty-one patients who continued smoking and 25 non-beta-blocked patients were considered to have an increased risk of recurrent cardiac events, as were patients with high initial lipid levels. In the smokers and non-beta-blocked patients total cholesterol decreased by 0.30 mmol.l-1 (P = 0.031) and 0.37 mmol.l-1 (P = 0.042) respectively and triglycerides by 0.28 mmol.l-1 (P = 0.058) and 0.13 mmol.l-1 (P = 0.11). Patients with high initial cholesterol and triglyceride levels had the largest cholesterol and triglyceride decrease, r = 0.43 (P = 0.0001) and r = 0.38 (P = 0.001) respectively. After adjusting for initial lipid levels, cholesterol (P = 0.036) as well as triglycerides (P = 0.034) decreased in patients without beta-blocker treatment whereas smoking no longer had an independent effect on lipid level decrease. HDL-cholesterol did not change in any group. Thus, after 4 weeks of exercise training lipid profiles were improved in patients with an increased risk of recurrent cardiac events. Beta-blocker treatment, however, seemed to hinder the beneficial effects of exercise training on lipid levels.