From January 1983 to April 1989, 39 children were diagnosed as suffering from primary peptic ulcer. Of these ulcers, 30 were duodenal, seven prepyloric, and two patients had a combination of both. Among 36 patients with H2-blocker therapy, 33 had treatment completed with ulcer healing assessed by endoscopic examinations. Sixteen patients (49%) had ulcer healing within a single 6-week course of treatment, whereas 17 patients (51%) required multiple 6-week courses. The latter group had a mean basal acid output (BAO) of 0.13 +/- 0.06 mmol/kg/h and a mean maximal acid output (MAO) of 0.48 +/- 0.12 mmol/kg/h, which is significantly higher (P less than .05 and P less than .005, respectively) than the mean BAO (0.08 +/- 0.06 mmol/kg/h) and mean MAO (0.31 +/- 0.11 mmol/kg/h) in patients whose ulcers healed within 6 weeks of treatment. Subsequent follow-up with endoscopy over a mean period of 1.8 years (range, 3 months to 6 years) showed 10 patients with recurrent ulcers. Life-table analysis showed a recurrence rate of 35% within 1 year after ulcer healing. Five patients required surgery for ulcer complications--obstruction (2), perforation (2), and bleeding (1). In two of these patients initial H2-blocker therapy was unsuccessful.