PURPOSE--To evaluate the effects of pravastatin on lipoproteins, Lp (a), apo B and apo A-I and its tolerability in primary hypercholesterolemic patients in our outpatient lipid clinic. METHODS--Twenty-two primary hypercholesterolemic patients were evaluated. They had all been treated previously with other hypocholesterolemic drugs, including the statins, forming a specific and homogeneous group with hypercholesterolemia and definite coronary risk. After 7 weeks with American Heart Association phase I diet and placebo drug, pravastatin was administered during 12 weeks. All patients received an initial daily dose of 10 mg for six weeks. After this period, this dose was increased to 20 mg. The levels of cholesterol, triglycerides, high-density lipoprotein, lipoprotein (a) and apolipoproteins A-1 and B were determined. RESULTS--No changes occurred with diet and placebo, but pravastatin at a daily dose of 10 mg, reduced significantly cholesterol level (7.22 per cent) LDL-cholesterol (13.08 per cent) and increased HDL-cholesterol (7.8 per cent). The results were better with 20 mg, achieving a reduction of (28.21 per cent) in cholesterol, (36.88 per cent) in LDL-cholesterol, (17.06 per cent) in apo B level and an increase of (10.06 per cent) in HDL-cholesterol. The smaller effect observed with the more commonly used dosage (10 mg/day) was most probably due to the characteristics of the sample with already established hypercholesterolemia, being thus dependent of higher concentrations of medications, as observed in previous treatments in our outpatient clinic. Side affects with this drug were rare. No biochemical changes were observed that would interrupt the continuation of therapy. CONCLUSION--Pravastatin was well tolerated and promoted favorable changes in the total cholesterol, LDL, apo B and cholesterol/HDL and LDL/HDL ratios of primary hypercholesterolemic patients