A series of six beta-adrenergic blocking drugs including propranolol, bufetolol, bunitrolol, pindolol, labetalol and acebutolol were examined for effects on adenylate cyclase, guanylate cyclase and calmodulin-dependent phosphodiesterase from heart. The adrenergic blocking agents had no apparent effects on basal activities of adenylate cyclase, guanylate cyclase and phosphodiesterase. The drugs blocked the enhancement of adenylate cyclase activity by isoproterenol, but not by guanine nucleotide or fluoride. The inhibitory effects of beta-antagonists were overcome by sufficiently large doses of isoproterenol. Sodium azide specifically required catalase whereas NaNO2 required cysteine to activate myocardial guanylate cyclase. Among beta-adrenergic blocking drugs tested, both pindolol and acebutolol inhibited the stimulation of guanylate cyclase by NaNo2 or N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). However, other beta-blocking drugs did not significantly affect the activation by NaN3, NaNO2 and MNNG. Several beta-antagonists, such as labetalol, bunitrolol, pindolol and acebutolol were also effective in blocking the activation of phosphodiesterase by calmodulin. The inhibitory effects of beta-adrenergic blocking drugs, i.e. pindolol and acebutolol upon either nitroso compound-stimulated guanylate cyclase or calmodulin-activated phosphodiesterase display little correlation with their potency as beta-adrenergic blocking agents. These data suggest that beta-antagonists may have another site of action which is not directly related to the control of catecholamine metabolism.