The effect of pindolol, a beta blocker with intrinsic sympathomimetic activity (ISA), on serum lipoprotein composition was studied in 13 patients admitted to the hospital for an attack of coronary heart disease. The control group consisted of 11 coronary patients without any beta-blocker therapy. Pindolol therapy was started during the stay in the hospital with a dose of 2.5-5.0 mg 2-3 times daily (mean dose 7.5 mg daily) and continued unaltered throughout the study. Serum samples were taken upon admission to the hospital and 4-6 months later, when the effect of acute coronary heart attack was stabilized. Initial serum cholesterol and HDL-cholesterol values were 6.82 mmol/l and 1.04 mmol/l, respectively. The ratio of HDL-cholesterol to total cholesterol (HDL/total) was 0.155 and serum triglycerides 1.78 mmol/l. During the pindolol therapy HDL-cholesterol and the HDL/total ratio increased by 12.5 and 11.2%, respectively, and the triglyceride level decreased by 16.9%. These changes, however, were not statistically significant due to interindividual variation. The results suggest that pindolol, unlike some other beta blockers, has no harmful effect on lipoprotein metabolism. This finding may have relevance when choosing a beta blocker for a patient with coronary heart disease.