Two hundred and ten patients (119 men and 91 women, mean age 54) with primary hypercholesterolemia (97% with total serum cholesterol greater than 240 mg/dl) were treated with lovastatin during 12 weeks in a placebo-controlled multicenter trial (10 cities and 21 investigators). All patients remained under an isocaloric low-fat, low-cholesterol diet throughout the study, and received placebo on a single-blind basis for the first 4 weeks (pretreatment period). Serum total cholesterol (TC), triglycerides (TG) and HDL-cholesterol (HDL-C) were measured at the beginning (week-4) and again at week 12. TC was also measured at weeks 0, 4, 8 and 12, while LDL-cholesterol (LDL-C) was calculated by a modification of Friedewald's formula. At the 5 clinic visits vital signs and body weight were recorded, and patients were questioned about adverse experiences. Safety laboratory tests (complete blood count, serum creatinine and creatinine phosphokinase, fasting plasma glucose, serum bilirubin, transaminases and alkaline phosphatase) plus a resting electrocardiogram (EG) and a complete (slit lamp) ophthalmologic examination were also carried out at weeks-4 and 12. During the treatment period lovastatin dosage was adjusted from 20 mg/day to 40 or 80 mg/day, if the TC value was greater than 200 mg/dL, with the resulting mean daily increasing doses of 28 mg (weeks 0-4), 37 mg (weeks 4-8), and 55 mg (weeks 8-12).(ABSTRACT TRUNCATED AT 250 WORDS)