Beta-adrenoceptor subtypes in detrusor and trigonal muscle of rabbit, canine and human urinary bladder were studied by in vitro techniques recording contractile force and by measuring intracellular cAMP content. The results of contractile studies were correlated with the intracellular cAMP levels. In the rabbit bladder, only beta 2-receptors were found in the detrusor though both beta 1- and beta 2-receptors were found in the trigonal muscle. In contrast, both beta 1 and beta 2-receptors were present in both detrusor and trigonal muscle of canine bladder. Human detrusor had only beta 2-receptors. Thus there are species differences in beta-adrenoceptor subtypes in urinary bladder smooth muscle.