The difference in autonomic nerve functions in vivo between the neurologically normal and the long-term parasympathetically denervated feline bladder and urethra was studied. For this purpose the vesical and urethral responses to electrical hypogastric and pelvic nerve stimulations and to various autonomic stimulating agents were investigated into. The nature of these responses was explored by different blocking agents. In the normal feline bladder phenylephrine caused a contraction. Noradrenaline always resulted in a bladder relaxation which was changed into a contraction after beta-adrenergic blockade. In the parasympathetically denervated bladders noradrenaline caused in most cats a bladder contraction without previous beta-adrenergic blockade. In the normal bladders hypogastric nerve stimulation always evoked an initial contraction and a subsequent bladder relaxation. In the parasympathetically denervated bladders, however, a novel response of a sustained bladder contraction was achieved. This contraction was blocked by a ganglionic or an alpha-adrenergic blocking agent, indicating that the reaction was mediated in preganglionic cholinergic fibres via postganglionic adrenergic neurons. The results indicat that parasympathetic denervation induces a change in the adrenergic receptor functions of the urinary bladder. Thus, in the neurologically normal bladder beta-adrenergic receptors mediating relaxation are in predominance while after long-term parasympathetic denervation alpha-adrenergic receptors mediating contraction dominate. No change in adrenergic receptor function was demonstrated in the urethra. alpha-Receptors mediating contraction were found to predominate both before and after parasympathetic denervation.