ipomoea imperati (vahl) griseb., convolvulaceae, is used in folk medicine for the treatment of inflammation, swelling and wounds, as well as to treat pains after childbirth and for stomach problems. administration of ethanol extract, lipid and aqueous fraction of i. imperati(300, 100 and 200 mg/kg) significantly inhibited the abdominal constriction in mice induced by acetic acid; increased the sleeping time evoked by pentobarbital sodium and showed a significant activity by inhibiting formalin-induced paw edema in mice. the same dose of i. imperatialso raised the pain of mice in the hot-plate test and increased the latency at all observation times. the pre-treatment of the animals with naloxone (5 mg/kg, i.p.) suggested the participation of the opioid system in the antinociceptive effect of ipomoea imperati.