Peptic ulcers treated with a proton pump inhibitor heal more quickly than those treated with a histamine H2 receptor antagonist. Although satisfactory healing without relapse is desirable in the medical treatment of peptic ulcers, the relapse rate after treatment with proton pump inhibitors has not been sufficiently studied. Up to now, several reports have suggested that peptic ulcers treated with omeprazole recur less frequently than those treated with H2 antagonists. Our experimental studies on angiogenesis in granulation tissue of acetic acid-induced gastric ulcers, gastric mucosal collagen synthesis etc., show that H2 antagonists have an inhibitory effect on wound healing, but that proton pump inhibitors do not. It is suggested, therefore, that proton pump inhibitors may at least have no undesirable effect on the natural history of peptic ulcer.