Three acetanilide and two pyrazolene derivatives were tested for anti-inflammatory effect on the edema of rat's hind-paws induced by the local injection of dextran, hyaluronidase, formaldehyde, histamine and 5-hydroxyptamine, and for histamine-release inhibitory effect on the rat receiving an intraperitoneal injection of ovomucoid which increases urinary output of histamine as a result of histamine release in the whole body. Phenacetin, acetanilide, aminopyrine, aminopropylone and butazolidine served as controls. GP-I, one of the pyrazolone derivatives (for formula cf. table 1), showed fairly marked supression on all 5 kinds of edema with effects comparable to aminopyrine and butazolidine. Acetanilide derivatives tested, also exerted marked inhibition on the edema other than by hyaluronidase or formaldehyde. All the compounds inhibited the histamine release due to ovomucoid injection, but no graded difference could be seen.