The effects of unilateral partial renal venous ligation on whole kidney and single nephron function were determined in anesthetized euvolemic Munich-Wistar rats using clearance, blood flow, and micropuncture techniques. Increased venous pressure (4-22 mmHg) reduced glomerular filtration rate (GFR) and renal plasma flow (RPF) to 60% of control values; filtration fraction (FF) was constant. Similar responses occurred in the superficial cortex, as evidenced by a 40% fall in SNGFR determined while intratubular pressure was maintained at the elevated precollection level. Fractional reabsorption by the proximal convoluted tubule remained constant, indicating maintenance of glomerulotubular balance. The contralateral kidney exhibit a diuresis and natriuresis while GFR and RPF were stable. In the experimental kidney single nephron glomerular plasma flow decreased by 35% due to increments in preglomerular and efferent arteriolar resistance. The transcapillary hydrostatic pressure gradient was unchanged since there were similar 7- to 8-mmHg increases in glomerular capillary and Bowman's space pressures. Filtration pressure disequilibrium was observed in control and experimental periods. Mean effective ultrafiltration pressure was similar in both periods. Specific values for the ultrafiltration coefficient (Kf) fell from 0.023 to 0.015 nl . s-1. mmHg-1. Accordingly, partial renal venous ligation produces ipsilateral vasoconstriction and a fall in GFR that is primarily due to a proportional decline in Kf.