This study examined the Influence of ginseng total saponins (GTS) on the analgestic action and tolerance development of pentazocine in mice. Pentazocine prolonged the latency to response in the tail flick rather than in the tail pinch test. The analgesic effect of pentaEocine was antagonized by naloxone and completely eliminated by pretreatment u·ith f-chlorophenylalanine (PCPA). GTS provented the pentasocine-incuced analgesia ann inhibited the development of tolerance to pentazocine. The antagonistic effect of GTS on the pentazocine-induced analgesia was abolished by 5-HTP, but not by L-DOPA. These results suggest that GTS inhibits the analgesic action of pentazocine by the interaction with serotonergic neuron.