The effects of narcotic analgesic agents and two inhalation anesthetics on intrabiliary pressure (IBP) were measured before and after morphine (0.2 mg/kg), meperidine (2 mg/kg), fentanyl (0.002 mg/kg), or pentazocine(1 mg/kg) given intramuscularly to guinea pigs, and after halothane (0.5, 1.0, 1.5, or 2.0 MAC) or enflurane (same range of MAC) administered by inhalation. All narcotics except pentazocine significantly increase IBP, the increases ranging from 85.7% for meperidine to 143.4% for fentanyl. Pentazocine had no effect on IBP. Peak IBP increases occurred between 9 and 18 minutes after administration. The elevation of IBP produced by narcotics was reversed by atropine (0.05 mg/kg). No statistically significant alterations of IBP were noted during halothane or enflurane anesthesia.