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Experimental tests cited herein have established that the deposits of inhaled particles may be highly concentrated at carinal ridges within lung bifurcations. Airway cells located at these sites will receive relatively massive doses of toxic substances and pharmacologic drugs. The deposition patterns, therefore, have immediate implications to risk assessment programs and aerosol therapy protocols. Herein, the software FIDAP was employed to study the effects of carinal ridge shapes upon fluid dynamics patterns. A series of welldefined geometric shapes (symmetric and asymmetric) were examined. For each case, a wide range of physiologically realistic flows were considered which corre-sponded to respiratory intensities for sedentary, light, and heavy activities. The results varied in a systematic manner. For example, at the lowest inspiratory flow rate of 14 L/min the effects were highly localized for all carinal ridge shapes, whereas at the highest inspiratory flow rate of 120 L/min the effects were propagated (i.e., to varying degrees) to distal regions. By relating fluid dynamics patterns to particle behavior, the results have inhalation toxicology and aerosol therapy relevance because, for example, bronchogenic carcinomas are selectively distributed within the tracheobronchial tree and certain receptors are known to be preferentially located at airway dividing sites.