Gastric acid suppression by use of either antacids or histamine H2-receptor antagonist therapy is the mainstay of stress ulcer prophylaxis. Available evidence indicating an antimicrobial role for gastric acid calls for the reevaluation of gastric acid suppression. A pH of greater than 4.0 leads to bacterial overgrowth and colonization of the upper gastrointestinal tract which has been associated with nosocomial pneumonia, bacterial translocation from the gut, systemic sepsis, and. multiple-organ failure. The availability of alternative therapy should discourage the routine use of acid-suppression therapy in the critically ill patient.