The H2-receptor is considered to mediate the stabilization of the membrane of mast cells by enhancing cAMP synthesis. In the present study, we investigated the effect of H2-receptor antagonists, i.e. H2-blockers, on nasal hypersensitiv-ity using a histamine nasal provocative test. A 7-day administration of cimetidine tended to lower the histamine threshold. Famotidine administered in the same way caused no significant decrease in the histamine threshold. Based on the above results, we postulate that famotidine should be preferred to cimetidine as an H2-blocker in patients with gastric and/or duodenal ulcers.