The objective of this study was to investigate the deposition characteristics of large, inhalable particles in rat nasal passages by determining the deposition efficiencies of these particles in a nasal mold of an F344 rat for steady-state and pulsating flow conditions. Particles with geometric diameters ranging from 0.5 to 4 microm and flow rates ranging from 100 to 900 ml/min were employed for simulated inspiratory and expiratory flow situations. The optically clear acrylic mold was fabricated from a life-size metal cast that comprised the nares, nasal cavity, pharynx, and larynx. Deposition efficiencies were calculated for each flow situation and plotted as functions of particle inertia. Inspiratory and expiratory deposition efficiencies were similar for a given flow condition. Deposition efficiencies for the cases of pulsating flows were markedly higher than those of steady flows. The results for pulsating flows indicated higher deposition efficiencies than were found in previous studies performed with live rats. These differences may be due to uncertainties in particle inhalability, clearance, and flow rate in the previous studies, as well as differences between the nasal geometries of live rats and the geometry of the nasal mold made from a postmortem cast. The results suggest that the pulsating nature of breathing is an important consideration when determining the deposition of fine and coarse particles.