Sulfur-containing amino acid concentrations were measured in serum of nine previously healthy adult trauma patients after 7 d of taurine-free parenteral nutrition and were compared with fasting serum concentrations in age- and sex-matched healthy subjects. Serum taurine concentrations in the patient group were depressed by 60% relative to control values (P less than 0.05) whereas serum methionine concentrations were significantly higher in the patient group. Serum cysteine concentrations were not significantly different between the two groups. This early decline in serum taurine concentrations in unsupplemented trauma patients suggests that taurine may be essential in the post-injury state.