SUMMARYThe cardiovascular effects of the synthetic amino terminal fragment of parathyroid hormone, PTH(l-34), were studied in intact conscious sheep. Physiological doses of bovine (b) PTH(l-34), 0-188, 0-376, 0-56 and 0 75 ,ug kg-' h-1 were infused in random order into conscious sheep for periods of 1 h each. Isotonic saline was infused as a control. Mean arterial blood pressure (MABP) decreased from 99-2 + 1-2 mmHg during the control infusion to 88-9 + 1-4 mmHg during infusion of the highest dose of PTH. Heart rate (HR) increased from 81 6 + 7 3 beats min-1 during the control infusion to 142 3 + 14-0 beats min-1 at the highest PTH dose and plasma renin activity (PRA) increased from 0-33 + 0 15 ng ml-1 h-1 to 1-54 + 0-46 ng ml-1 h-1. Cardiac output (CO), calculated by an indirect method, increased to 176 + 28 % of the control values. The changes in all four parameters were dose dependent. Renal blood flow (RBF) increased during the PTH infusion period.