Sinomenine (i.p.) produces antinociception in the hot plate and tail flick tests in male rats at 40 mg/kg, but not at lower doses (10 or 20 mg/kg). At 10 to 40 mg/kg Sinomenine does not produce any observable side effect such as sedation, allergy or motor impairments. At 80 mg/kg, Sinomenine is mildly sedative in rats. Antinociception is also seen mice at 60 min following 80 mg/kg i.p. Sinomenine, but not at lower doses (20 or 40 mg/kg), in the tail flick test. Sinomenine at 80 mg/kg i.p. does not produce any observable side effects in mice. I.p or p.o. Sinomenine at 40 or 80 mg/kg dose-dependently reduces mechanical hypersensitivity in nerve injured mice. I.p. Sinomenine at 40 mg/kg, but not lower doses or vehicle, significantly decreases mechanical and cold allodynia for up to 240 min without producing motor deficits or sedation. At doses of 10 to 40 mg/kg, Sinomenine dose-dependently increases the paw withdrawal threshold. In non-chronic constriction injury (CCI) healthy rats, Sinomenine at the dose range of 10 to 40 mg/kg does not change the immobility behavior in the forced swimming test.