During severe hepatic insufficiency, serum amino acid profile is modified with an increase of aromatic amino acids (AAA) (Tyrosine and Phenylalanine) and methionine concentrations and a decreased value of 3 branched chain amino acids (BCAA) (leucine, isoleucine and valine). These observations have been confirmed after hepatic surgery in experimental and clinical studies. In experimental models, after 10, 32, 68, 77 or 90% hepatectomy in Wistar rats, the BCAA/AAA ratio (R) is correlated with the extent of hepatectomy: r = 0.74, p < 0.001; with the post-operative interval time (8, 24, 32, 48, 168 or 240 hours): r = 0.60, p < 0.001 and with the liver weight when animals are sacrificed: r = 0.64, p < 0.001. In clinical studies, 26 patients have undergone 60 to 80% hepatectomy for primary or secondary tumors of the liver and R is determined on the immediate post-operative day and every day during the first post-operative week. Liver regeneration is followed by single photon emission computerized tomoscintigraphy on days 0, 7 and 30 with assessment of hepatic growth index (HGI) estimated by the ratio: liver mass on day 7 or 30/remnant liver mass on day 0. On post-operative day 7, R is 1.61 +/- 0.3 (normal: 3.5 +/- 0.51). Mean liver volume is 60 +/- 11% and HGI is 1.9 +/- 0.3. On this day, a correlation is found between R and HGI (r = 0.76). On post-operative day 30, HGI is 2.34 +/- 0.50, mean liver volume is 89.6 +/- 0.9% and R is 2.02 +/- 0.65.(ABSTRACT TRUNCATED AT 250 WORDS)