Patients on regimen C are children, aged 4 to 18 years. Patients inhale a radiolabelled (technetium 99m) monodisperse iron oxide aerosol. Radiation deposited in the patient's lungs is monitored. Patients are randomized to receive one of 4 different aerosols (vehicle; UTP; amiloride; or UTP plus amiloride), which is inhaled for 20 minutes. Patients are followed 24 hours after aerosol exposure.