Shock is often the final pathway through which a variety of pathologic processes lead to cardiovascular failure and death. The purpose of this study is to determine the value of serum lactate as a predictor of outcome in shock patient. We investigated the correlation between serum lactate levels and mortality in 42 patients whose systolic BP were below 90mmHg on initial presentation. Serial arterial blood lactate levels were measured on admission and every 4 hours for one day. 29 patients were survived. Initial BP was not different between survivors and nonsurvivors. Lactate levels were significantly higher in the nonsurviviors than survivors(p<0.05). But, there were no difference in lactate clearance between survivors and nonsurvivors(p>0.05). 24 hours survival rate was 42.9% in patients whose lactate levels were above 100mg/dl initiaUy and statistically significant in comparison with patients whose lactate levels were below 100mg/dl(p<0.01). The latters' survival rate was 85.7%. Our data suggest that initial lactate level could be correlated with the prognosis of shock patient.