Pachygone, a member of the family Menispermaceae, is a small genus of scandent shrubs which are distributed mainly in the Indo-Malaysian region. Pachygone ovata is the only species available in India, and it grows in the sandy seashores of the Coromandel coast. The dried fruits of this plant are used by local people for destroying vermin and stupefying fish (1, 2). No phytochemical work on any of the Pachygone species has yet been reported. The chemical constituents isolated from different parts of the plant and identified are N-methylcrotsparine (1), reticuline (2), reticuline N-oxide (3), (+)-quercitol (4), liriodenine (5), trilobine (6) and coclaurine (7). Of these compounds, reticuline N-oxide is a new amine oxide which has not been reported earlier either as a natural product or as a synthetic compound. The major leaf alkaloid reticuline was subjected to pharmacological investigation. In doses ranging between 10-20 mg/kg, i.p., reticuline produced signs of central nervous system stimulation characterized by piloerection, irritability, alertness, compulsive biting of the cage wires, and tremors. All mice exhibited Straube's tail phenomenon. When the dose was increased to 30-40 mg/kg, there were tetanic convulsions characterized by hind limb extension. The convulsions were reflex in nature. Pretreatment of the mice with mephenesin (10 mg/kg, i.p.) totally prevented reticuline-induced convulsions. In the interictal period the mice appeared to be sedated having decreased motility and ptosis. Reticuline (5 mg/kg, i.p.) significantly (P <0.001) potentiated hexobarbitone induced hypnosis, the mean sleeping time (in min±S.E.M.) being 56.2±16.3 and 31.3±4.9 in the reticuline-pretreated and control hexobarbitone groups, respectively. However, this potentiation was not apparent with a higher dose of reticuline (20 mg/kg, i.p.), where the sleeping time was 23.7±3.9 (P>0.05). Reticuline significantly (P <0.001) enhanced locomotor activity in a dose of 10 mg/kg, i.p. The 30 min cumulative actophotometer recording in control and reticuline-treated mice (5 in each group) was 286±56 and 486±92, respectively. The rise of rectal temperature with 5, 10, and 20 mg/kg, i.p., over pre-drug control level (35.5±1.2°C mean±S.E.M.) was +0.36±0.12, +0.69±0.19 and +1.1±0.16, respectively. All values were statistically significant (P < 0.05) as compared to controls. Reticuline produced a dose-related hyperthermic response in rats. Reticuline produced a mild to moderate degree of antinociceptive activity in doses of 10 and 20 mg/kg, i.p. The increase in the latent period of tail flick response (mean ±S.E.M.) was 7.8±1.1 and 11.9±1.6 sec, respectively. Both values were statistically significant (P <0.001). Reticuline significantly (P <0.05) potentiated the lethal effect of amphetamine (10 mg/kg, i.p.) in aggregated rats. In the control group there was 10% death noted at 4 hours after amphetamine administration, whereas in the reticuline-treated group there was 60% mortality. Tetanic convulsions induced in frogs after reticuline (40 mg/kg in ventral lymph sac) were present in decorticated frogs as well as in animals whose midbrain and medulla were ablated. However, the convulsions were abolished after destruction of the spinal cord. The L.D.50 of reticuline in mice was 56±8 mg/kg, i.p. The results suggest that reticuline has central stimulant, analgesic, hyperthermic, and convulsant actions. The convulsions were strychnine-like and were prevented by a central muscle relaxant and abolished after ablation of the spinal cord. The pharmacologic profile of activity of reticuline thus qualitatively closely resembles that of thebaine (10, 11). This finding is interesting in view of the fact that reticuline is the established precursor (12) of morphothebaine alkaloids. There is room for speculation that reticuline undergoes oxidative transformation to thebaine or a thebaine-like molecule to elicit this pharmacological activity.