Morphological studies during the treatment of patients with nasal polyps with beclomethasone dipropionate aerosol for one year showed a trend towards a decrease in the number of eosinophils in nasal smears and falls in the increased concentrations of albumin, IgG and IgE in the nasal secretion. No change in the histological picture of the polypous tissue except increased density was observed. By scanning electron microscopy, no change in the surface structure of the nasal mucous membrane was noted. As morphological studies did not reveal any sign of adverse effects, beclomethasone dipropionate may be regarded as a valuable drug in the treatment of nasal polyps. The indications for its clinical use and supplementary therapy are discussed.