Background: Distressed behavior is common in infants and is often attributed to gastroesophageal reflux (GER) or food protein intolerance.Objective: To examine the effect ofa hypoallergenic amino acid-based infant formula (AAF) on distressed behavior and GER symptoms in infants who failed to respond to extensively hydrolyzed formula and antireflux medications.Study design: Nineteen distressed infants (9 boys and 10 girls; median age, 5.0 months) with presumed GER underwent gastroscopy (n = 17) and esophageal 24-hour pH monitoring (n = 14). Double-blind placebo-controlled (DBPC) formula challenges of AAF versus previously best-tolerated formula were conducted.Results: Nine infants had histologlc evidence of esophagitis, and 9 had inflammatory changes in the stomach and/or duodenum. Symptoms remitted in all infants within 2 weeks of the start of feeding with AAF. On DBPC challenge after a median period of 3 months of receiving AAF, 12 infants were intolerant to active formula (distress score, 287 vs 580 min/wk, P = .01; symptom score, 23.1 vs 36.1, P = .03). Seven infants did not relapse and were considered tolerant (distress score, 470 vs 581, P = .77; symptom score, 29.5 vs 20.2; P = .89).Conclusion: Treatment with AAF may reduce distressed behavior and symptoms of GER in infants with food protein intolerance. (J Pediatr 2000;136:641-647)