In this study, the retention and clearance of particles instilled onto the epithelium at two sites in the nasal cavity were examined. Polystyrene microspheres (3 μm geometric diameter) were labeled with141Ce or85Sr and instilled simultaneously on the maxillary and ethmoid turbinates of beagle dogs. The retention and clearance patterns of the microspheres were followed for 30 d after instillation. Tissue samples, excreta content, and autoradiography of the radiolabels provided the basis for defining the fate of the microspheres or the radiolabels dissolved from the microspheres. Early nasal mucus velocity was significantly faster (p < 0.05) from the maxillary turbinate region (2.5 ± 0.7 mmlmin, mean ± SE) than from the ethmoid turbinate region (0.6 ± 0.4 mmlmin). Retention at both instillation sites at 30 d after instillation was approximately 0.7% of the amount initially instilled. Radioactivity was excreted primarily via the feces during the first few days. Radiolabel measured in urine and tissues other than turbinates was small (<0.05% of the initial burden), indicating minimal dissolution of the radiolabel from the particles. Autoradiographs of turbinate tissue revealed particles sporadically located in the epithelial submucosa. From these data, it was concluded that a significant difference in early clearance for particles exists between the ethmoid and maxillary turbinates, but there was no difference in the fraction of particles retained in these two areas for long periods of time.