Safety evaluation of LB71350, a new HIV-1 protease inhibitor, was performed in mice, rats and dogs. For the general behavior of mice, LB71350 at an oral dose of 200 mg/kg did not show any significant effects on muscle tone and locomotor activity. In terms of central nervous system, at oral doses of 200 mg/kg and 1000 mg/kg, LB71350 inhibited acetic acid-induced pain response approximately 41% and 83% of control. respectively. At oral doses of 200 mg/kg and 500 mg/kg, it reduced the rectal body temperature in rats. Pentylenetetrazole-induced seizure in mice was slightly potentiated by oral administration of LB71350 at doses ranging from 200 mg/kg to 1000 mg/Ag. Single or five day treatment of LB71350 doubled the hexobarbital- induced sleeping time in mice at oral doses ranging from 50 mg/kg to 500 mg/kg. It did not cause any effects on gastric secretion and acidity in rat at oral doses of 200 mg/kg and 1000 mg/kg and also it did not change intestinal motility in mice up to 1000 mg/kg. Blood coagulation indices such as prothrombin time (PT), activated partial thromboplastin time (aPTT), and thrombin time (TT) in rats were not affected by the treatment of LB71350 up to 500 mg/kg. LB71350 caused no significant effects on the cardiac output, stroke volume, heart rate, and mean blood pressure when infused intravenously to the anesthetized rats and dogs. Taken together, LB71350 at high oral doses caused significant pharmacological effects on the central nervous system and the hexobarbital-induced sleeping time.