To explore the effects of renal hemodynamics upon urinary albumin excretion, sequential changes in perfusion pressure and/or flow were performed in isolated perfused rat kidneys. Elevation of perfusion pressure from 90 to 130 mm Hg increased renal flow from 48.9 +/- 1.1 to 54.3 +/- 1.4 ml/min and glomerular filtration rate (GFR) from 0.37 +/- 0.03 to 0.81 +/- 0.06 ml/min (p less than 0.001). Despite more than a doubling in GFR, albumin excretion remained unchanged (from 252 +/- 53 to 167 +/- 36 micrograms/min, p not significant), resulting in a decreased fractional clearance of albumin (theta) from 0.009 +/- 0.002 to 0.004 +/- 0.005 ml/min (p less than 0.01). To dissociate the effects of flow from those of pressure, angiotensin II was infused to decrease renal flow from 49.9 +/- 0.6 to 38.7 +/- 0.6 ml/min (p less than 0.001), while keeping perfusion pressure constant at 96 +/- 1 mm Hg. Although GFR was essentially unchanged (from 0.59 +/- 0.02 to 0.65 +/- 0.05 ml/min, p not significant), albumin excretion increased from 68 +/- 8 to 151 +/- 21 micrograms/min (p less than 0.001) and theta rose from 0.002 +/- 0.000 to 0.005 +/- 0.001 (p less than 0.02). Whole kidney hemodynamics acutely affect renal excretion of albumin in isolated kidneys.