In studying antireflux medications, we may use tests for assessing symptoms of gastroesophageal reflux to establish or confirm a diagnosis of reflux disease and to evaluate whether study subjects are improving with therapy. Symptom assessment questionnaires need to be validated, results need to be reproducible, and the outcome variables measured need to be clinically relevant. Other outcomes for clinical trials include measures of esophagitis: histologic (morphometric) measures in infants and endoscopic and histologic visualization in older children. Intraesophageal pH monitoring studies may be useful for obtaining pharmacodynamic data.