Of 16 children with primary duodenal ulcer, 11 had complete relief of symptoms with initial full dose cimetidine therapy. After stopping cimetidine two of these 11 relapsed, six are in remission and three occasionally complain of abdominal pain requiring antacids. The remaining five children showed no improvement at all. Only one out of the 16 children showed side-effects due to cimetidine. Although there was wide variation in dosage of cimetidine and duration of therapy, no significant difference was noted in the dosage regimen of responders and non-responders to cimetidine. We suggest, full dose cimetidine 20 to 40 mg/Kg/day for 4 to 8 weeks, followed by 8 mg/Kg nocte daily for another 4 to 8 weeks.