Sixty-one cases of the Zollinger-Ellison syndrome, encountered over a 2-year period, have been treated with cimetidine, half of them for over 1 year. Two-thirds of the patients responded to 300 mg of the drug every 6 hr by mouth. Others required up to 600 mg every 6 hr. In adequate doses the drug was highly effective: it controlled pain and dyspepsia, restored weight, abolished diarrhea, and allowed healing of ulcers and other inflammatory conditions. Missed or reduced doses led to rapid return of symptoms. Progression of the basic neoplastic process, with associated secretory drive, was unimpeded. Patient acceptance of the drug was 100 percent, and apart from minor transient abnormalities, gynecomastia (5 cases) and liver dysfunction (3 cases), which resolved while treatment continued, no serious adverse effects were seen. Of 61 patients 48 are still on the drug, 3 who were well controlled were treated surgically, 5 died for reasons unrelated to therapy, and 5 had significant problems. The drug provides an alternative to total gastrectomy and can be recommended with confidence for the suitably selected patients. The drug was also beneficial in some cases of the short bowel syndrome, systemic mastocytosis, and endogenous hyperhistaminemia due to leukemia.