We investigated the anti-allergic effect of tea-leaf saponin (TLS), which was a mixture of saponins separated from the leaves of Camellia sinensis var. sinensis, in guinea pigs and rats. TLS (20-100 mg/kg) dose-dependently inhibited experimentally-induced asthma, and ID50 was 61.7 mg/kg. TLS (20-100 mg/kg) dose-dependently inhibited a 48 h homologous PCA (passive cutaneous anaphylaxis) reaction, and the inhibitory effect was similar to that of tranilast. TLS (1-100 microg/ml) also inhibited the release of antigen-induced leukotriene (LT) C4 from sensitized guinea pig lung samples in a dose-dependent fashion, but did not prevent histamine release. TLS (0.01-0.5 microg/ml) inhibited histamine release from rat peritoneal mast cells induced by compound 48/80. At higher concentrations, TLS elicited histamine release. These findings suggest that TLS may be a useful protective agent against clinical allergy, and that the inhibitory effects of TLS on mediator release are in some way related to its inhibitory effect on experimentally-induced asthma and PCA reaction.