In a surgical intensive care unit a controlled clinical trial for stress ulcer prophylaxis with cimetidine was performed in patients with severe polytrauma. Severe polytrauma was defined as affection of at least 3 body cavities (head, thorax, abdomen), 2 body cavities and 1 extremity fracture, 1 body cavity and 2 extremity fractures of 3 extremity fractures. An extremity fracture was defined as a fracture of a long bone i.e. humerus, femur. Initially the trial was planned as randomized double-blind using a fixed sample size. It was executed as a sequential single-blind study only and stopped for ethical reasons before the bounderies were reached and was analyzed according to the advice of an external referee using Fisher's exact test (p < 0.025). Cimetidine was highly effective in preventing stress ulceration in severe polytrauma patients, but mortality was the same in the cimetidine and in the placebo group.