We investigated the effects of escins Ia, Ib, and IIb isolated from horse chestnut, the seeds of Aesculus hippocastanum L., and desacylescins I and II obtained by alkaline hydrolysis of escins on acute inflammation in animals (p.o.). Escins Ia, Ib, IIa, and IIb (50-200 mg/kg) inhibited the increase of vascular permeability induced by both acetic acid in mice and histamine in rats. Escins Ib, IIa, and IIb (50-200 mg/kg) also inhibited that induced by serotonin in rats, but escin Ia didn't. Escins Ia, Ib, IIa, and IIb (200 mg/kg) inhibited the hind paw edema induced by carrageenin at the first phase in rats. Escin Ia (200 mg/kg) and escins Ib, IIa, and IIb (50-200 mg/kg) inhibited the scratching behavior induced by compound 48/80 in mice, but escin Ia was weakest. Desacylescins I and II (200 mg/kg) showed no effect. With regard to the relationship between their chemical structures and activities, the acyl groups in escins were essential. Escins Ib, IIa, and IIb with either the 21-angeloyl group or the 2'-O-xylopyranosyl moiety showed more potent activities than escin Ia which had both the 21-tigloyl group and the 2'-O-glucopyranosyl moiety.