The findings about mechanisms regulating production and excretion of urodilatin [ANP-(95-126)], a member of the atrial natriuretic peptide (ANP) family, are controversial. To elucidate a possible relationship between arterial blood pressure and renal urodilatin excretion, we studied the effects of different perfusion pressures on urine flow (UV), urinary sodium (U_NaV), urinary potassium (U_KV), and urodilatin excretion (U_UROV), and the concentration of urodilatin in the perfusate (P_URO) of isolated perfused rat kidneys. Kidneys were perfused for 180 min with constant perfusion pressures (80 and 120 mmHg, respectively; each, n = 4) in a closed circuit system. Samples of urine and perfusate were taken every 30 min. Mean UV, U_NaV, U_KV, and U_UROV values were significantly higher with a perfusion pressure of 120 mmHg than with 80 mmHg, whereas P_URO did not change significantly. Serial measurements revealed no direct relation of U_UROV with either U_NaV or UV. This suggests that renal perfusion pressure is a determinant of U_UROV and that urinary and venous effluent concentrations of urodilatin (probably production) are not coupled directly and that U_UROV and U_NaV may dissociate during acute variations of sodium excretion and UV.