Fibre-optic bronchoscopy was performed in 21 patients with small cell bronchogenic carcinoma who demonstrated a complete radiographic regression of their chest lesions after 3-4 months of combination chemotherapy. Fifteen patients showed abnormalities at the site of the original tumour consisting of nodular elevations, narrowing of bronchi and/or fibrous strands or membranes. Microscopic evidence of residual cancer was obtained in 3 cases. In 3 out of 8 patients who underwent a further bronchoscopy after 18 months of treatment, disappearance of nodules was noted at the later examination. Persistent bronchial narrowing was observed in patients who became disease-free 2-yr survivors. It is concluded that tumour regression may be accompanied by scar formation, which complicate the interpretation of post-treatment abnormalities, and that further regression of intrabronchial lesions may occur beyond 3-4 months.