Arterial blood lactate concentration at the end of fixed volume hemorrhage was evaluated as a predictor of survival in unmedicated chronically instrumented immature swine. Compared to basal values, 8.4 +/- 4.5 mg/dl (means +/- SD, n = 52), hemorrhaged animals (n = 71) with a lactate of 43.9 +/- 37.1 mg/dl lived while animals (n = 65) with a lactate of 106.5 +/- 40.4 mg/dl died. Lactate concentration at the end of hemorrhage successfully predicted survival (81.0%). Prospective evaluation, using a blood lactate concentration of 125 mg/dl (n = 27), showed a predictive success of 81.0%. Arterial plasma lactate concentration at the end of hemorrhage thus may be used to predict survival in the conscious swine.