K12.148 (INN: lifibrol), a new cholesterol synthesis inhibitor, was studied in healthy volunteers to evaluate tolerance/safety, the effects on lipids, and pharmacokinetics. In a sequential block design the doses of 150, 300, 600, or 900 mg, given once daily in the morning for 14 consecutive days, were examined in 40 healthy young males (8 active drug and 2 placebo per group, randomized) under well-controlled conditions. Total and LDL cholesterol serum levels decreased significantly in the 300, 600, and 900 mg groups ( -13.4% , - 23.8%, −25.6%, and −14.7%, −33.3%, −34.8% respectively), whereas no significant change was seen with placebo and 150 mg. The antiatherogenic index Apo A-I/B increased in a dose-dependent manner between 300 and 900 mg. Changes in HDL cholesterol and triglycerides were not statistically significant. The study compound was tolerated well, and safety laboratory parameters did not show any relevant alterations. K 12.148 might be a very effective drug for the treatment of hypercholesterolemia.