Previous studies have demonstrated that parathyroid hormone (PTH) and its 1–34 amino terminal fragment possess a hypotensive action in vivo which appeared to be direct and dose-dependent. However, attempts to demonstrate the phenomenon in isolated vascular tissue have been minimally successful at best. The present study reports that bovine PTH-(1–34) can relax isolated rat tail artery helical strips precontracted by either arginine vasopressin, depolarizing concentrations of potassium chloride, or norepinephrine. The phenomenon occurs in a dose-dependent manner and is not dependent upon the presence of the endothelial lining of the vessels. These studies support the hypothesis that bovine PTH-(l-34) produces a direct vasorelaxant action mainly in small arteries.