One highly promising adjunct to acute treatment of peptic ulcer disease is long-term maintenance therapy with H2-receptor antagonists. Ranitidine, an agent that has been shown to be as effective as cimetidine in the acute therapy of healing ulcers, has also been evaluated for long-term prevention of ulcer recurrence. In such studies, 12 months of maintenance therapy with 150 mg of ranitidine at bedtime could sustain 75 to 90 percent remission in patients with healed duodenal ulcers and as high as 93 percent remission in patients with healed gastric ulcers. The relapse rate during a second year of maintenance was even lower, and most ulcers that did recur during these studies could be healed with a second course of twice daily ranitidine therapy. Relapse rates during maintenance with ranitidine are equal or better than comparable reports with cimetidine, about 20 percent for both drugs, and both have been well tolerated with a minimum of serious adverse reactions. As is now widely known, ranitidine appears to have substantially fewer side effects, including absence of interference with the microsomal enzyme metabolism of other drugs. The more convenient dosage schedule of ranitidine may be important for patient compliance with initial therapy of peptic ulcer disease, and the greater duration of ranitidine antisecretory effects may enhance effectiveness of long-term maintenance therapy by providing more complete inhibition of nocturnal acid secretion.