BACKGROUND: H-2-receptor antagonists are commonly used for stress ulcer prophylaxis on intensive, sive care units. However, there is evidence that via the route of an elevated gastric pH, followed by bacterial overgrowth and subsequent tracheal aspiration, pneumonia could occur. In line with this assumption total gastrectomized patients should develop a very high incidence of pneumonia, which is actually not the case. We therefore formulated the hypothesis that stress ulcer prophylaxis with H-2-receptor antagonists does not lead to an increased pneumonia rate. METHODS: A total of 158 patients with mechanical ventilation greater than or equal to 48 hours of a surgical intensive care unit were randomized to the following groups: A, placebo (n = 57); B, pirenzepine (3 x 10 mg intravenously, n = 44); and C, ranitidine (3 x 50 nag intravenously, n = 57). RESULTS: The pneumonia rate in ranitidine-, pirenzepine-, and placebo-treated patients is 10 of 57, 10 of 44, and 112 of 57, respectively. CONCLUSIONS: Pneumonia rate is not adversely affected by H-2-receptor antagonists in stress ulcer prophylaxis. Am J Surg. 1998;176:453-457. (C) 1998 by Excerpta Medica, Inc.