An electromyographic study of the responses of the pelvicalyceal border which is the pacemaker region of ureteral peristalsis, and of the renal pelvis and ureter to dobutamine and terbutaline, beta 1- and beta 2-adrenergic stimulants, respectively, was performed using isolated canine pelviureteral preparations. The beta 1-adrenergic stimulant produced a marked enhancement of discharge potential in the pacemaker region, but, in the renal pelvis and ureter, it did not evoke any noticeable response. Application of the beta 2-adrenergic stimulant led to disappearance of discharges in the renal pelvis and ureter, whereas the pacemaker region continued to exhibit regular discharges. These findings seem to suggest the presence in the pelvicalyceal border of a group of cells which, unlike other smooth muscle cells, respond to beta-adrenergic agents in a fashion similar to the cardiac pacemaker, namely, stimulated by beta 1-adrenergic stimulants and not inhibited by beta 2-adrenergic stimulants.