Effects of diltiazem on isolated ureter and coronary artery of the dog were compared with those of glycerol trinitrate (GTN). Diltiazem (DZ) (10–9–10–6M) decreased the force and frequency of ureteral rhythmic contractions evoked by potassium or phenylephrine in a concentration-dependent manner, and relaxed potassium-contracted coronary artery strips. The dose dependence of the inhibitory effects of diltiazem was similar on the ureter and coronary artery. GTN (10–7–10–5M) also showed similar inhibitory effects, but these were more pronounced on the coronary artery than on the ureter.