Abstract Treatment of rat reticulocytes with isoproterenol resulted in the heterologous desensitization of adenylate cyclase, causing a reduction in NaF/AlCl 3- and guanylyl 5′-imidodiphosphate (Gpp(NH)p)-stimulated activities as well as in activity stimulated by β-adrenoceptor agonists. Desensitization was also induced by dibutyryl cyclic AMP and 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7), an inhibitor of cyclic AMP-dependent protein kinase (protein kinase A), prevented the isoproterenol-induced desensitization, suggesting the involvement of protein kinase A in the desensitization. G s in the desensitized cell membrane was activated by treatment with Gpp(NH)p or NaF/AlCl 3 in the presence of Mg 2+. The activated state, the G s-C complex, was gradually shifted to the basal state, i.e. the G s-C complex was dissociated by removal of Mg 2+. The rate constant of the dissociation was increased in the desensitized cell membranes (0.074 min −1) as compared with that in the control cell membranes (0.022 min −1) The half life of the G s-C complex, calculated from the rate constant, was decreased during the process of desensitization. The results indicate that reduction in the stability of the G s-C complex is related to heterologous desensitization. Agents which increase the level of cyclic AMP in the cell also reduced the stability of the complex. The potency of such an effect was in the following order; isoproterenol ∼ NaF/AlCl 3(k = 0.071 min −1) > forskolin (0.039 min −1 > Mn 2+ ∼ dibytyryl cyclic AMP (0.030 min −1). The former two activate G s.and form G s-C complex, while the latter two cause intracellular cyclic AMP accumulation without activation of G s. It may be deduced from this order that the reduction of the stability depends not only on the increase in the cyclic AMP level but also on the level of G s-C complex formed.