Clinical findings suggest that bronchogenic tumors have a predilection for certain airway locations in man. Aerosol deposition studies with laryngeal-tracheobronchial casts and models indicate that such sites in situ correspond to 'hot spots' of deposition, and that cells located at carinal ridges may be particularly susceptible to development of bronchial carcinomas. For cigarette smokers, the etiology of lung cancer may be affected by synergistic interactions following exposures to naturally occurring indoor radon progeny. The problem is exacerbated for workers in the uranium mining and milling industry due to additional exposures to radioactive dust particles. The paper suggests that heterogeneous local deposition patterns in bronchial airways, concomitant with increased radiation exposure to targeted cells, may be the relevant factor in lung cancer induction, and implies that enhanced activity sites should be accounted for in risk assessment carcinogenesis models.