We investigated the changes in the membranous β-adrenoceptor-adenylate cyclase system in the right ventricle, left ventricle and interventricular septum during the progress of monocrotaline-induced right ventricular hypertrophy and failure. Theβ-adrenoceptor density was decreased in hypertrophied right ventricle 2 to 4 weeks after treatment. When the rats showed symptoms of right ventricular failure 4 weeks after treatment, theβ-adrenoceptor density was decreased in the interventricular septum. Both basal and forskolin-stimulated adenylate cyclase activities were decreased in the right ventricle at 3 and 4 weeks, and in the interventricular septum at 4 weeks, after treatment, which indicates that the catalytic activity of adenylate cyclase is reduced. Changes in isoproterenol plus Gpp (NH) p- or sodium fluoride-stimulated adenylate cyclase activity were generally similar to those in basal activity. These data indicate that a chamber-specific decrease inβ-adrenoceptor density begins in the early stages of right ventricular hypertrophy, and thatβ-adrenoceptor density and adenylate cyclase activity in the interventricular septum are decreased in the advanced stages of heart failure in monocrotaline-treated rats.