1. We examined the effects of phosphonium, [[4-[[2- [[bis(cyclohexylamino)methylene]amino]-3-(2-naphthalenyl) 1-oxopropyl]amino]-phenyl]-tributyl, chloride, monohydrochloride (WIN 64338), a novel, nonpeptide bradykinin B2 receptor antagonist, on bradykinin-induced contractions of guinea-pig isolated ileum, and guinea-pig and ferret trachea. 2. WIN 64338 potently and competitively antagonized ileal contractions, in response to bradykinin, exhibiting a pA2 value of 7.97 +/- 0.10. The compound was without effect on contractions elicited by methacholine, a muscarinic receptor antagonist. Thus, WIN 64338 is a competitive and selective antagonist of ileal B2 receptors. 3. In contrast, WIN 64338 was completely without effect on bradykinin-induced contractions of guinea-pig or ferret trachea. Thus, even at a concentration of 1 microM, which was sufficient to cause a 100 fold decrease in ileal sensitivity to bradykinin, WIN 64338 failed to shift the bradykinin log concentration-response curves in trachea isolated from either species. 4. These data confirm that WIN 64338 represents the first reported nonpeptide antagonist of guinea-pig ileal B2 receptors. They also provide additional evidence for heterogeneity of bradykinin receptors within the same species (guinea-pig) and, furthermore, indicate that the tracheal bradykinin receptor (B3?) is different from that in ileal tissue (B2).