A new hypolipidemic agent, lovastatin, hydroxy-methyl-gultaryl coenzyme A reductase inhibitor was administred to 25 patients with primary hyperlipidemia 20 to 40 mg daily for 12 weeks and sequential changes of serum lipid profile were analysed as follow. 1) Mean average at baseline period of serum total cholesterol, triglyceride, HDL and low desity lipoprotein cholesterol were 271, 179, 51 and 185 mg/dl respectively. 2) Total cholesterol showed 20% decrease at 4th week and 23% decrease at the end of 12th week while low density lipoprotein cholesterol decreased 31% and 33% respectively. 3) Triglyceride dropped 7% at 8th week and 3% at 12th week. High density lipoprotein cholesterol increased 4% at 4th week and showed 2% decrease at the end of study. 4) Only one patient complained of moderate abdominal pain, which subsided after 2 weeks drug withdrawal. In conclusion, lovastatin was well tolerated and effective, in the treatment of primary hyperlipidemia.