Bladder and urethral responses to filling and to subcutaneous bethanechol are dependent upon intact sacral innervation. Acute selective sectioning of nerve roots in chloralose anesthetized cats was used to compare the sacral innervation requirements for the support of these responses. The detrusor was found to require primarily intact S2 roots although an S2 root on one side could, alone, subserve a weak, unsustained detrusor reflex. The urethral reaction to bladder filling required an afferent sacral pathway through either S1 or S2 roots. The sustained bladder response to subcutaneous bethanechol required greater sacral innervation than the detrusor reflex inasmuch as the S2 segment could subserve this response in only half the cases, and unilateral rhizotomy L7-S3 eliminated the response in half the cases. Both treatments, however, were compatible with a preserved detrusor reflex. The urethral constriction response to subcutaneous bethanechol required an intact sacral afferent pathway through either the S1 or S2 segments. In conclusion, the detrusor and urethral reflex responses to bladder filling and subcutaneous bethanechol require a certain amount of intact sacral innervation through S1 and S2 which is least for the detrusor reflex and greatest for the bladder response to subcutaneous bethanechol.