Twenty-two adult patients suffering from common variable immunodeficiency (CVID) and sixteen patients with selective IgA deficiency were examined with regard to the mucocilliary function of the nose. The surface structures of the nasal mucosa, e.g. cell distribution and degree of destruction and metaplasia, were judged from scanning electron microscopy of nasal biopsies. Bacteria were isolated from nasopharyngeal swabs. The results of the clinical and morphological investigations were analysed with regard to the duration of the disease and possible benefit of adequate prophylaxis with immunoglobulin. It was found that patients with CVID had a slower mucociliary transport rate and more extensive mucosal damages than patients with selective IgA deficiency. Most likely these alterations were due to repeated infections as patients who had had few infections or adequate immunoglobulin prophylaxis (CVID patients) had better mucociliary function and showed less extensive mucosal changes. Potentially pathogenic bacteria in the nasopharynx were found in equal numbers in both patient groups.