The pharmacological profile of a new histamine H2-receptor antagonist, 2-(3-(3-(1-piperidinylmethyl)phenoxy)propylamino)-4 (3H)-quinazolinone (NO-794), was studied. NO-794 was a potent and selective histamine H2-receptor antagonist in the guinea-pig atria and gastric mucosal cells. NO-794 (1 X 10(-5) M) did not interact with H1-, muscarinic and beta 1-receptors. In guinea-pig atria, antagonism of NO-794 was unsurmountable. The onset of action of NO-794 was slow, and this antagonism was apparently irreversible not only on the guinea-pig atria but also on the gastric mucosal cells. In addition, NO-794 inhibited gastric acid secretion in pylorus ligated rats when administered intraduodenally. These results indicate that NO-794 is a powerful and unique histamine H2-receptor antagonist and may be useful in the treatment of peptic ulcer.