Decreased renal sodium excretion was observed 2 to 5 days after a two-thirds hepatectomy (Hx) in male Wistar-Hannover rats (200-300 g; N = 10 per group). This fall occurred after normalization of serum liver enzymes by the second day. Hepatocellular dysfunction was demonstrated by a pronounced and transient increase of about 1150% in plasma alanine aminotransferase (ALT), 500% in aspartate aminotransferase (AST), 250% in alkaline phosphatase (ALP) and in serum direct bilirubin levels, which were about six-fold higher than in sham-operated (SH) animals on the first and second days after hepatectomy. On the basis of the renal clearance of lithium in partially hepatectomized rats, there was a sustained decrease in fractional sodium excretion between the second (SH: 0.053 +/- 0.008% vs Hx: 0.023 +/- 0.008%) and fifth days (SH: 0.040 +/- 0.006% vs Hx: 0.027 +/- 0.009%) post-hepatectomy. This decrease was accompanied by a rise in the absolute (68 +/- 5.2 mumol min-1 100 g body weight-1) and fractional (85.2 +/- 1.4%) proximal sodium reabsorption rates compared to sham-operated rats (53 +/- 3.5 mumol min-1 100 g body weight-1 and 80.6 +/- 1.1%), but a return to baseline excretion levels was observed by the tenth experimental day. These changes occurred in the absence of any alterations in creatinine clearance, sodium filtered load, hematocrit and total blood volume. Further studies are required to establish the mechanisms of interaction between renal tubule sodium handling and liver function.