IgG1, antibody-mediated homologous passive cutaneous anaphylaxis at 1.5 h (1.5-hour PCA) was elicited in the ears of mice and the effects of different drugs were studied. The reaction, as measured by the amount of extravasated dye, was inhibited by antihistamines, antiserotonins, cyclic AMP-elevating agents, tranilast and ketotifen, but not by an SRS-A antagonist (FLP 55712), lipoxygenase inhibitors, cyclooxygenase inhibitors and disodium cromoglycate. These results suggest that the pharmacological profile of 1.5-hour PCA resembles that of 48-hour PCA mediated by IgE antibody in the mouse ear.