Pamidronate (aminohydroxypropylidine bisphosphonate, APD) is an effective agent for treatment of Paget's disease of bone, and it has also been thought to be effective for treatment of osteoporosis. We desired to study a newer, time-release preparation of pamidronate, and carried out a placebo-controlled, double-masked study of postmenopausal osteoporosis. The original formulation was in a rapidly dissolving gelatin capsule. We encountered four episodes of esophagitis in 49 enrolled patients. We therefore discontinued treatment with this preparation and later began the study again using a standard tablet preparation. We encountered an additional case of erosive esophagitis in 1 patient of 40 receiving this tablet preparation. No patient was receiving concomitant medication which could cause esophagitis. Two of the patients gave a past history of hiatal hernia and 1 gave a history of gastric ulcer 27 years previously. The diagnosis of esophagitis was confirmed in all cases by endoscopy. Healing of the esophagitis promptly ensued after discontinuation of the pamidronate and the use of antacid medication.