Electrical activities have been recorded in a preparation consisting of the pelvic region and the upper ureter of the guinea pig. Train field stimulation of the pelvic region evoked a train of nerve action potentials followed by a multiphasic smooth muscle action potential after a latency of about 2.5--8.0 sec. This smooth muscle response was abolished by tetrodotoxin and dibucaine, and also by cholinergic blocking agents. The response was furthermore, inhibited by decreasing Ca/4 concentration and increasing Mg/+ concentration in Tyrode solution. This is therefore considered to be the response synaptically evoked by cholinergic fibers in the pelvic region. Mechanical activities have been investigated on the same preparations by the Magnus method. Acetylcholine (10(-7)--10(-4) g/ml) produced a group of twitch responses which were antagonized by cholinergic blocking agents. The responsiveness of the preparations to acetylcholine was markedly decreased by removal of the pelvic region. Cholinesterase activities in the calyx-pelvis and upper ureter have been estimated by the biochemical method. A preparation consisting of calyx-pelvis exhibited twice the enzyme activity as compared with the upper ureter. These results suggesteds that there is a cholinergic innervation in the pelvic region of the guinea pig ureter which also takes part in control of the ureteric activity.