In 10 patients with the nephrotic syndrome (NS) and edema persisting despite a NaCl-poor diet, the effect of a single infusion of hyperoncotic albumin (75 g) on NaCl excretion was studied. 6 patients had minimal lesions, and 2 patients were studied twice. On half of the occasions the glomerular filtration rate was reduced. Blood volume (BV), calculated from plasma volume and hematocrit, was slightly elevated before infusion, and increased to 136 and 120 of normal at 4 and 20 h after it, respectively. Plasma renin activity (PRA) and plasma aldosterone (PA) both decreased to suppressed levels at 20 h after infusion. Sodium excretion increased from 9.2 ± 7.6 μEq/min before, to 31.0 ± 22.4 (0–4 h) and 43.1 ± 36.3 μEq/min (4–20 h) after infusion. In 6 of these patients clearance studies were done before and after the infusion, maximal free water clearance being used as marker for distal NaCl reabsorption. Proximal fractional NaCl reabsorption was elevated before (94.9 ± 1.4) and decreased after the infusion (92.8 ± 1.7). Distal fractional NaCl reabsorption was also elevated before (93.0 ± 6.4), but unaltered after infusion (93.0 ± 5.6). Thus, after marked expansion of BV and suppression of PRA and PA, sodium excretion remained low despite the present edema. The results indicate that in many patients with the NS, including minimal lesion NS, intravascular hypovolemia is not the sole cause of sodi
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