BACKGROUND: The lactate concentration should be used to examine the severity of sepsis or any state of shock. This study was conducted to investigate the prognostic power of the lactate clearance, as adjusted for time, between the survivors and nonsurvivors of patients with severe sepsis or septic shock. METHODS: The study was performed on 67 patients over 16 years old and who were admitted to the intensive care unit (ICU) with severe sepsis or septic shock. They were divided into the survivors (n = 37) and nonsurvivors (n = 30). The blood lactate concentrations were assayed at intervals ranging from 8 to 24 hours and the APACHE III scoring was done daily for 2 weeks or until discharge or death. The lactate clearance, as adjusted for time, was defined using the following formula: [(the maximal lactate concentration - the normal lactate concentration)/the time to normalize the lactate concentration] x 1,000. RESULTS: There were no significant differences of age, gender and the length of the ICU stay between the survivors and non-survivors. There were significant difference of the time to measuring the maximal serum lactate concentration (3.2 +/- 12.3 hours vs. 28.8 +/- 64.6 hours, respectively; p = 0.037), the lactate clearance, as adjusted for time (132.27 +/- 112.88 mol/L . hour vs. 59.67 +/- 72.60 mol/L . hour, respectively; p = 0.002), the lactate clearance during 24 hours (46.0 +/- 26.3% vs. 22.6 +/- 45.6%, respectively; p = 0.018) and the APACHE III score (67.6 +/- 22.7 vs. 83.9 +/- 21.6, respectively; p = 0.005) between the survivors and non-survivors. The lactate clearance, as adjusted for time and the APACHE III score were the predictive factors for survival on the logistic regression analysis (odd ratio 0.987; p = 0.028 vs. odd ratio 1.046; p = 0.006). CONCLUSIONS: Lactate clearance, as adjusted for time, could be used as a prognostic index, as well as the APACHE III score, for patients with severe sepsis or septic shock.