It has been suggested that the quantity of amino acids perfused is a pathogenetic factor in total parenteral nutrition (TPN)-associated hepatotoxicity. However, the effect of the qualitative pattern of amino acid solutions has not been studied. Rats on parenteral nutrition for 5 days received 10.2 g of dextrose and 3.4 g of amino acids daily. Bile flow (microliter/min/g liver protein) after administration of Vamin was 16.2 +/- 0.8, which was similar to that in controls given chow and dextrose iv, but it was significantly higher (p less than 0.001) than those on Travasol (12.3 +/- 0.8). The decrease in bile flow was not related to the large concentrations of alanine and glycine present in Travasol. However, the addition to Travasol of serine present only in Vamin increased bile flow significantly. Bile acid secretion rate, biliary lipid constituents, calcium, sodium, and glucose showed little change. In contrast, alpha-amino nitrogen was increased (p less than 0.05) in Vamin-perfused animals. Steatosis was noted in only a few animals in the Travasol group, and was not associated with an increase in the triglycerides content of the liver. Glycogen and protein content of the livers did not differ. The data show that the composition of amino acid solutions may be a determinant of TPN-induced cholestasis and suggest that the presence of methyl donor amino acids may have a protective effect.