We studied the effects of sulfasalazine(SSZ) on anaphylaxis. SSZ was found to exhibit a inhibitory activity on the compound 48/80-induced anaphylaxis. SSZ also inhibited local a naphylaxis activated by anti-dinitrophenyl(DNP) IgE. Moreover, SSZ dose-dependently inhibited histamine ralease in rat peritoneal mast cells activated by compound 48/80 or anti DNP IgE. We investigated the effects of SSZ on cAMP of rat peritoneal mast cell. The level of cAMP in rat peritoneal mast cells, when SSZ was added, transiently and significantly increased approximately 16-fold compared with that of basal cells. These results suggest that the antianaphylactic action of SSZ may be associated with an increase in the intracellular cAMP content of the mast cells as the result of an inhibition of the cAMP phosphodiesterase.