Sepsis, the commonest cause of late death following severe trauma, is related in part to inadequate uptake of amino acids (AA) and synthesis by the liver and other central tissues of proteins essential to immunological defense. Since 'central plasma clearance rate' of amino acids (CPCR-AA) has been found to reflect these functions, serial measurements of CPCR-AA were made in 32 seriously injured patients of whom ten died (31%), nine of sepsis. The mean Index Severity Score on admission for survivors was 31 +/- 1.8 and in deaths 34 +/- 3.9 (N.S.). The blood plasma AA concentrations were not significantly different. However, early in the course before the onset of infection, CPCR-AA in surviving patients was 227 +/- 30 and in those who ultimately died 83 +/- 24 ml/M2/min (p less than 0.001). Later during sepsis the values of CPCR-AA were 176 +/- 28 and 85 +/- 14 ml/M2/min, respectively (p less than 0.01). Thus CPCR-AA appears to be of value as an indicator of amino acid utilization by central tissues and as a predictor of survival or death following severe trauma.