Administration of solutions high in branched-chain amino acids (BCAA) has been advocated in patients with severe liver failure; however, the effect of this treatment on the process of liver regeneration is still unclear. In the present study using rats we investigated the influence on liver regeneration of infusing solutions differing in amino acid content. After 75% hepatectomy, rats were infused via jugular vein with one of the following solutions: Sol A) 10% dextrose, Sol B) 10% dextrose + 3% amino acids (22% BCAA), Sol C) 10% dextrose + 3% amino acids (35% BCAA). Liver regeneration was estimated by measuring the incorporation of 3H-thymidine into DNA at five different time points after the operation. Peak regeneration occurred earlier in rats infused with the BCAA-enriched solution compared to animals infused with the standard amino acid solution or with dextrose alone. The increased incorporation of 3H-thymidine into DNA at 24 hr in rats infused with the BCAA-enriched solution was associated with elevated plasma levels of BCAA and decreased concentrations of tyrosine, phenylalanine, and methionine in comparison with the other two treatment groups. These results suggest that liver regeneration in rats can be accelerated by administering a parenteral nutrition solution tailored to normalize the deranged pattern of plasma amino acids associated with compromised liver function.