The butanolic fraction (BT-II) derived from the aqueous crude extract was prepared from aerial parts of Baccharis trimera and assessed in anti-inflammatory, analgesia, and ulcerogenesis models. Intraperitoneal pretreatment with lyophilized BT-II, at doses ranging from 40 to 100 mg/kg, markedly inhibited carrageenan- and dextran-induced inflammation (70.4-90.8% and 25.7-71.3%, respectively) and weakly decreased C16-paf- and arachidonic acid-induced swelling (24.9-36.7% and 0-30.6%, respectively). No effect was observed, at the same doses, on zymosan-induced edema. The intraperitoneal examination indicates that the anti-phlogistic action of BT-II was not due to an irritating effect at the injection site. Besides, BT-II reduced abdominal constrictions in mice following injection of acetic acid: at 50 mg/kg, it gave 67.4% inhibition and, at 100 mg/kg, 95.1%. The ulcerogenic assay showed that the incidence of ulcers after BT-II i.p. treatment was 2/6 at 50 mg/kg and 6/6 at 100 mg/kg. Ulcerogenic indices were 1.3 +/- 0.5 and 2.7 +/- 0.8, respectively. These results indicate that B.trimera shows strong anti-inflammatory and analgesic properties which seem to be due, at least partly, to the inhibition of prostaglandin biosynthesis. The chromatographic separation of BT-II monitored by bio-assay (carrageenan-induced edema test in mice) was carried out. The active constituents were found to be mainly saponins in which echinocystic acid (or its enantiomer) is the major aglycone, and also rutin.