Thirty three children aged 2 to 42 months (mean 9 months) with gastro-oesophageal reflux and peptic oesophagitis took part in a treatment trial comparing cimetidine (20 mg/kg/day) with an intensive regimen of antacids (Maalox, 700 mmol (mEq)/1 X 73 m2/day). All children were evaluated clinically and by radiology, acid reflux test, and endoscopy. After 12 weeks of treatment all were again evaluated clinically, by pH measurement, and endoscopy. Twenty nine children, 15 on antacid and 14 on cimetidine, completed the trial. Eight patients on antacid and seven on cimetidine were cured; five on antacid and six on cimetidine improved; and two patients on antacid and one on cimetidine underwent surgery. Both groups of children showed a statistically significant reduction in the score of clinical, pH, and endoscopic variables after treatment. Lower oesophageal sphincter pressure before treatment did not correlate significantly with the final total score. Antacids in large quantities are as effective as cimetidine in medical treatment of gastro-oesophageal reflux and peptic oesophagitis.