Pipethiadene, a prophylactic of vasomotoric headaches of the series of 4,9-dihydrothieno(2,3-c)-2-benzothiepine derivatives, shows a peripheralpharmacological profile of an antiallergic agent. The experiments in rats showed a high antianaphylactic effect of pipethiadene in the passive cutaneous anaphylaxis (PCA) test. Pipethiadene also exerted intensive antianaphylactoid action in rats on the liberator of histamine, compound 48/80, on dextran, and in the use of a combination of ovalbumin with indomethacin. In comparative pharmacological experiments with pizotifen and cyproheptadine an attempt was made to estimate the relative role of histamine and 5-hydroxytryptamine 5-HT) mediators in the employed experimental procedures in rats.