Purpose - To compare the effects of lovastatin and gemfibrozil in patients with primary hyperlipidemias. Patients and Methods - Forty patients with cholesterolemia over 200 mgldl and triglyceridemia not higher than 350 mp/dl, excluded secondary causes, were selected. Twenty patients received lovastatin and 20 gemfibrozil. In order to establish the lipid profile, blood samples were taken after 2 months without medication, after 4 weeks of diet and placebo and after 6 and 12 weeks active treatment. Biochemic profile was determined before and after the treatment with active drug. Results - Thirty nine patients completed the study. Total and LDL-cholesterol were significantly reduced (p < 0.05) by both drugs but lovastatin had greater effect. Only gemfibrozil reduced triglycerides significantly. Neither drug had significant effects on HDL-cholesterol. The tolerance was satisfactory; only one patient (using gemfibrozil) needed to stop the treatment due to gastrointestinal side effects. The biochemic profïle did not present any significant alteration. Conclusion - Both drugs produced useful effects on the lipid profile. Lovastatin produced greater reductions of total and LDL-cholesterol, while gemfibrozil was more active reducing triglycerides. Neither drug changed significantly the HDL-cholesterol