Stress ulcer bleeding is a serious complication of critical illness and is associated with increased morbidity and mortality. For the prophylaxis of stress ulcers, antacids, H2-blockers, or sucralfate are prescribed. While H2-blockers inhibit the secretion of gastric acid, sucralfate appears to provide protection without reducing levels of gastric acid. Inhibition of acid secretion increases gastric pH, allowing bacterial overgrowth of the stomach by Gram negative bacteria, which colonize the pharynx and trachea and increase the risk of nosocomial pneumonia. For this reason, H2 blockers appear disadvantageous, though they offer adequate prophylaxis for stress ulcer bleeding. As it does not increase gastric pH, sucralfate provides adequate protection against Gram negative gastric overgrowth, however its prophylactic efficacy is not generally accepted. Therefore, we compared the H2-blocker ranitidine to sucralfate in the prophylactic treatment of stress ulcer bleeding and studied the incidence of positive bacteriological findings in the blood and bronchial secretions of the two groups. In a randomized study, 84 patients undergoing general intensive care received either ranitidine (6 x 50 to 6 x 100 mg daily i.v.) or sucralfate (6 x 1 g via gastric tube or per os). Both groups were comparable with respect to age, underlying disorders, and factors predisposing to the development of stress ulcers.(ABSTRACT TRUNCATED AT 250 WORDS)