Prevention of gastrointestinal stress lesions by cimetidine or pirenzepine was investigated in a double blind study of trauma patients in an intensive care unit. Cimetidine or pirenzepine were administered intravenously to 55 consecutive randomized patients. All were checked by endoscopy on admission and 8 days later. 5 therapy failures were found in each group. Patients with more than 5 erosions and/or ulcerations were classified as failures. A side effect encountered was sinus tachycardia in 4 of 27 patients treated with pirenzepine. Overall, a trend towards fewer stress lesions was found in the pirenzepine protected group.