Blood volume and whole kidney and single nephron function were evaluated 2 and 10 days after nephrotoxic serum nephritis (NSN) induction in Wistar rats. Progressive proteinuria, hypervolemia and edema were observed in NSN rats. Sodium retention was associated with a progressive depression of single nephron glomerular filtration rate and elevated fractional tubular reabsorption rates. Since hypervolemia rather than hypovolemia was observed in this study, edema formation must have been a consequence of intrarenal rather than extrarenal phenomena.