The effects of butyl 3'-(1H-tetrazol-5-yl)oxanilate (WP-833), a new antiallergic drug, on type I to type IV allergic reactions were investigated by employing various animal models. WP-833 (i.v. and p.o.) dose-dependently inhibited homologous or heterologous passive cutaneous anaphylaxis (PCA) mediated by rat or mouse immunoglobulin E (IgE) in rats. Homologous PCA caused by guinea pig IgE was also inhibited by WP-833. In addition, WP-833 had inhibitory actions upon homologous PCA induced by rat or guinea pig IgG. However, WP-833 showed no inhibition of rat skin reactions caused by histamine, serotonin and bradykinin, contrasting with the inhibition of prostaglandin E1-induced skin reaction. Furthermore, both adrenalectomy and propranolol treatment exerted no influences on the inhibition of IgE-mediated homologous PCA in rats by WP-833. In contrast to above findings demonstrating that WP-833 clearly inhibited type I allergic reaction, systemic Forssman shock in guinea pigs and reversed cutaneous anaphylaxis in rats (type II), passive Arthus reaction in rats (type III), and contact dermatitis and tuberculin reaction in mice (type IV) were unaffected by WP-833 even in higher doses than in those capable of completely inhibiting type I allergic reaction.