Twenty-five patients admitted to intensive or high-dependency surgical care units were randomized to receive ranitidine intravenously 50 mg every 6 hours for 8 days or no ranitidine. All had septicemia or intra-abdominal sepsis, with body temperature greater than or equal to 38.5 degrees C for more than 48 hours despite comprehensive medical and/or surgical treatment. Cell-mediated immunity was assessed by skin testing with seven common delayed type hypersensitivity antigens applied on days 1, 4 and 7 and all tests were read at 48 hours, i.e. on days 3, 6 and 9. The ranitidine/non-ranitidine regimen was initiated on day 1 and continued until day 9. Severity of illness was evaluated before and 3, 6 and 8 days after initiating the study, using the APACHE II scoring system. The scores before and during the study were similar in the ranitidine and non-ranitidine groups. Delayed type hypersensitivity improved in patients treated with ranitidine (p less than 0.001), but was unchanged in the untreated group (p greater than 0.7). These observations may suggest potential beneficial effects of ranitidine therapy in patients with trauma-induced immunosuppression.