Isotonic and isometric cystometry was used in anesthetized cats, some of which had their spinal cord severed previously. Reflex contraction of the bladder was obtained by electrical stimulation of the central stump of the first three sacral dorsal roots. Only in one animal out of 14, bladder contraction followed stimulation of the distal stump of sacral roots when the ventral roots had been cut. Stimulation of the distal stump of ventral roots showed that the major efferents to the bladder from the sacral cord traveled through S3. Surprisingly, consistent but smaller bladder contractions developed when the distal stumps of the ventral roots of L5 and L6 were stimulated. It was impossible to establish whether these represented activation of the detrusor or other vesical muscle, and pharmacological tests failed to differentiate between the lumbar and sacral-driven contractions.