Picumast is a prophylactically active anti-allergic compound which combines inhibition of mediator release and action. The activity profile of picumast differs clearly from that of known prophylactic anti-allergic drugs such as DSCG and ketotifen. Other inhibitory actions of picumast in addition to its Histamine H1 receptor -antagonism (and that of its metabolites M2 and M1) may be the cause of the suppression of immediate and late phase allergic reactions in animals as well as allergic rhinitis and bronchial responsiveness and symptom scores in asthmatic patients. In the rat, picumast inhibited carrageenin edema but was inactive against other types of inflammation. Picumast dihydrochloride cannot be considered as an anti-inflammatory drug in general, since it was inactive against adjuvant arthritis in rats and did not inhibit cotton pellet granulomas.