A study was made of 106 children between 1 and 15 years of age (mean 6 years) with recurrent upper and lower airways infections since birth. Nasal mucociliary transport (NMT) velocity was determined in all subjects by the Tc99m-labeled seroalbumin technique. In 42 children, NMT was found to be altered. In this group of patients the technique was repeated in a period of between 1 and 2 years later. In 23 cases (55%) transport had normalized, while in 19 (45%) it remained altered. Recurrent pneumonia and constant rhinorrhea were more frequent in this group. Situs inversus was only detected in 2 of these patients. Pathology showed ciliary ultrastructure, the absence of dynein arms and microtubule alterations. The absence of cilia was observed in some patients. Normal cilia were also encountered in children with persistently altered nasal mucociliary transport.