The methanol extracts of Aconitum roots have shown inhibition of increased vascular permeability induced by acetic acid and of hind paw edema produced by carrageenin in mice. The extract of A. carmichaeli has been fractionated, monitored by the capillary permeability test, to yield the aconitines as active principles. The aconitines have inhibited the increased vascular permeability induced by acetic acid in mouse peritoneal cavity and that induced by histamine in rat intradermal sites, and the hind paw edema formation induced by carrageenin in rats and mice at low doses. The benzoylaconines have exhibited inhibitory effects on the aforementioned acute inflammations but at the higher doses. The aconitines have reduced the granulation tissue formation of the chorio-allantoic membrane of the chick embryo. On the other hand, the Aconitum alkaloids have elicited no effects on the ultraviolet erythema formation in guinea pigs at lower doses than the lethal ones and failed to show positive responses on the vascular permeability in the granuloma pouch and on adjuvant arthritis in rats at the doses employed.