The purpose of this study was to determine the most critical substrate or metabolic parameters from among a large number of plasma substances which would predict patient survival or demise in the trauma-septic state. Twenty-five septic patients (14 survivors, 11 nonsurvivors) with 102 analyses were evaluated. Levels of amino acids were analyzed on a pattern basis by use of fractional concentrations (Z values), the ratio of the individual amino acid concentration to the total concentration of either the essential or nonessential amino acids according to the amino acid type. Patients who did not survive (in contrast to survivors) had significantly lower Z values for Ser, Glu, Gly, Val, He, Leu, and Arg, and higher Z values for Asp, Thr, Asn, Pro, Ala, Met, Phe, His, and Trp, all of which indicated marked pattern distortions between the two patient sets. Concentrations of plasma substances reduced in patients who did not survive were taurine, alpha- 1-acid glycoprotein, and ceruloplasmin, and increased were alpha-aminobutyrate, urea, glucose, free fatty acids, triglycerides, lactate, retinol-binding protein, cortisol, and glucagon. Using the same patient data base discriminant analyses, a further form of pattern evaluation, were conducted between the patient groups. With these analyses, patients who later succumbed could be identified 9 days before demise with 99% certainty from a single plasma analysis profile. The variables with greatest discriminant power, in decreasing order, were urea, lactate, the sum of the nonessential amino acids (negative), alpha-aminobutyrate, glucagon, glucose, Z glutamine, Z aspartate, Z asparagine, ornithine (negative), AO2, alpha-1-acid glycoprotein, Z valine (negative), ceruloplasmin (negative), alpha-2-HS glycoprotein, pyruvate (negative), and Z phenylalamine. Alterations in metabolism as reflected in plasma substrate patterns are thus critical indicators of a degrading septic state.