Severe sepsis and septic shock are a major health problem worldwide and among critically ill patients in particular. Beyond the identification of the likely focus of infection and of the organisms responsible, treatment with appropriate antibiotics, and drainage of the focus itself, when possible, early, and aggressive hemodynamic resuscitation is recommended for the treatment of septic patients. The identification of severe sepsis is based on clinical signs but also on laboratory findings. Among these, sepsis-associated hyperlactatemia (SAHL) has been recently promoted as a way of identifying patients with `cryptic’ shock who require focused, early goal-directed therapy. The physiologic source of lactate production during sepsis is now a matter of research. Recent data indicate that other potential non-hypoxic reasons can lead to SAHL. Human studies have did not succeed to exhibit a correlation between hyperlactatemia and any markers of tissue hypoxia or other indices of reduced cellular oxygenation. If insufficient perfusion/oxygenation was the reason of hyperlactatemia, methods to increase systemic or local oxygen supply to supranormal values should correct hyperlactatemia. Conclusively, if, as seems from previous observations, SAHL is not a result of low oxygen, another justification is needed.