Mucosal biopsies from the pharynx, right main stem bronchus and right lower lobe were obtained during flexible fiberoptic bronchoscopy and were examined with light microscopy (LM) and electron microscopy (EM) in 10 asthmatics after 11 months' (range 7-15 months) treatment with high doses of inhaled budesonide via the Nebuhaler, i.e. 1600 micrograms daily. Results were compared with biopsies from 10 controls suspected of having focal, malignant lung diseases. Visual inspection of the tracheobronchial tree showed no signs of atrophy, ulcerations or thrush patches, and LM and EM showed no specific signs of mucosa and connective tissue atrophy; however, epithelial desquamation was seen in the asthmatics. No complications were observed.