Voiding induced in conscious monkeys by infusion of sterile saline into the bladder via a chronically implanted bladder catheter was stable over many months. Artefact-free recordings of electrical activity were obtained from the bladder neck and dome of these animals during bladder filling and voiding. Characteristic voiding electromyograms were recorded from both sites but were seen first in the record from the neck. Small doses of methyl-atropine abolished both voiding and the electromyograms; evoked responses to sacral ventral root stimulation were similarly prevented. Therefore the bladders of both man and monkey are very sensitive to atropine, unlike the bladders of most other animals.