An asymmetric multiple-path model of particle deposition in the lung airways developed previously (S. Anjilvel and B. Asgharian, 1995, Fundam. Appl. Toxicol. 28, 41-50), was extended to calculate deposition of fibers in the rat lung by replacing the deposition efficiency expressions for particles with those of fibers. The effects of various parameters such as breathing parameters or fiber dimensions on deposition were studied. Fiber deposition fraction for one single breath was calculated per acini, lobe, and region of interest in the lung. The results were compared with one other model prediction and with data available in the literature. Good agreement between the model predictions and other studies was found.