1) Chronic administration of morphine hydrochloride in the drinking water of mice induced physical dependence. Jumping and diarrhea, two signs of withdrawal, were produced by intraperitoneal (IP) injection of naloxone."n2) Baclofen, bicuculline and picrotoxin decreased the number of mice's jumping episodes and frequency of diarrhea."n3) Muscimol decreased jumping but not diarrhea."n4) The data indicate that GABA-Ergic system is possibly involved in the morphine physical dependence, but further studies are required to elucidate the roles of GABA-A or GABA-B receptor sites in physical dependence.