To evaluate the effectiveness of somatostatin versus combined cimetidine and pirenzepine in the treatment of upper gastrointestinal (GI) bleeding of peptic origin, a multicentre controlled, prospective, randomized and double blind trial has been undertaken in 60 subjects. Strict selection criteria were followed. All subjects were diagnosed by endoscopy during the first 18 h after admission. Endoscopic stigmata of recent haemorrhage were also evaluated. Sixty-five per cent of the subjects presented with severe upper GI bleeding (blood pressure less than or equal to 100 mmHg, pulse rate greater than or equal to 110, haematocrit less than or equal to 30 per cent), and in 71.6 per cent stigmata were found. Thirty patients (Group 1) received a somatostatin infusion (250 micrograms/h continuously during 120 h) and 30 patients (Group 2) received cimetidine (200 mg IV every 4 h for 5 days) and pirenzepine (10 mg IV every 8 h for 5 days). Both groups were homogeneous for sex, age, backgrounds, bleeding source, grade of bleeding (moderate or severe) and presence or not of stigmata. Bleeding stopped in 27 subjects of Group 1 (90 per cent and in 20 subjects of Group 2 (66.67 per cent) (P less than 0.05, chi 2 test). The time until the bleeding stopped was significantly shorter in patients of group 1 (3.44 +/- 0.53 h) than in patients of group 2 (8.12 +/- 1.94 h) (P less than 0.05, Mann-Whitney U test). The number of blood units required for Group 1 (2.26 +/- 0.35) was significantly lower than the one required for Group 2 (3.90 +/- 0.51) (P less than 0.005, Wilcoxon test). Significant differences were not observed between the two groups regarding cross-over subjects, re-bleeding, surgery (P = 0.0635, Fisher's exact test) and hospital stay. The mortality of the trial was 5 per cent. There was no toxicity during somatostatin, cimetidine or pirenzepine infusion. In conclusion, somatostatin was more effective than cimetidine plus pirenzepine in the control of severe upper GI bleeding of peptic origin, with a lower interval time to stop bleeding and reduced transfusion requirements.