An open clinical trial was performed to test the efficacy and side effects of Pravastatin(Mevlotin(R)), HMG-CoA reductase inhibitor, administering 5mg twice daily for 12weeks in 30 patients of hypercholesterolemia in out patient clinics, Pusan National University Hospital. The total cholesterol, triglyceride and HDL-cholesterol were measured with enzyme methods and LDL-cholesterol was calculated indirectly by Friedewald formula. The result obtained were as follows: 1) The degree of change at the end points compared with baseline pretreatment levels were 26.1% fall in serum total cholesterol.36.6% fall in LDL-cholesterol, 20.8% fall in triglyceride and 14, 6% rise in HDL-cholesterol. And the rate of improvement more than moderate degree were 90.0% in total cholesterol(the fall of 10% or more), 53.3% in triglyceride (the fall 20% or more) and 33.3% in HDL-cholesterol(the rise of 7mg% or more). 2) The total cholesterol/HDL-cholesterol and LDL-cholesterol/HDL cholesterol ratios were decreased significantly from 6, 4+/-0.7 to 4.2+/-0.5(34.4%) and from 4.5+/-0.7 to 2.5 +/-0.4(44.4%) respectively. 3) The greatest fall in serum total cholesterol and LDL-cholesterol were observed in 2 weeks after administrating drug and thereafter fell gradually and maintained until 12 weeks of endpoint, but HDL-cholesterol showed significant rise from the 4 weeks of administration. On the other hand triglyceride showed remarkable fall in the measured values from the 4 weeks but statistical significance was observed only in 10 and 12 weeks after administration owing to wide individual variation of values. 4) There observed the tendency that the higher the initial pretreatment levels the greater the degree of fall in total cholesterol and triglyceride. 5) Neither side effects nor abnormal laboratory findings were shown during the period of observation. The results suggest that Pravastatin will be a useful and safe drug in the treatment of hyperlipidemia.