A double-blind cross-over study was performed on 12 men sith stable angina pectoris in order to determine the effect of antilipolytic treatment on exercise tolerance and exercise-induced electrocardiographic changes. The men were exercised to the onset of anginal pain using a reproducible and standardized ergometric load. A nicotinic acid analogue was used to reduce plasma free fatty acids and free glycerol before and during exercise testing and to eliminate their post-exercise rise. This was associated with significant reduction of exercise-induced ST segment depression (p less than 0-005), though there was no significant difference in the duration of exercise before the oneset of pain. A change in the prportions of lipid and carbohydrate for oxidation by the ischaemic myocardium, making relatively more glucose available, is a likely explanation.