To investigate the effects of repeated silver nanoparticle exposure on the nasal septum respiratory mucosa, 6-week-old SD rats were exposed to silver nanoparticles at concentrations of fresh air control, low-dose (1.73 x 10(4)/cm, 0.5 microg/m(3)), middle-dose (1.27 x 10(5)/cm(3), 3.5 microg/m(3)) and high-dose (1.32 x 10(6)particles/cm(3), 61 microg/m(3)) in an inhalation chamber for 6h per day, 5 times a week for 28 days. The animals were sacrificed after the 28 days of exposure period. Histochemical staining, including periodic acid Schiff (PAS), alcian blue (AB) pH 2.5, and high iron diamine-alcian blue (HID-AB) pH 2.5, was used to evaluate changes in the mucosubstance properties of the goblet cells in the respiratory epithelium. In a histopathological study, the nasal cavity and lungs from the exposed groups exhibited no remarkable changes compared to the control group. However, a slight increase in the neutral mucins was noted for all the silver nanoparticle-exposed groups when compared to the control group, although without statistical significance. Nonetheless, the size and number of goblet cells containing neutral mucins increased significantly in the groups exposed to silver nanoparticle at middle- and high-dose (P<0.05). While the densities of the stained mucosubstances showed no difference among the exposed groups, the amount of neutral mucins did tend to increase slightly, although acid mucins including sulfomucins and sialomucins showed no change in any of the exposed groups. Therefore, the present results did indicate that silver nanoparticles have an influence on the neutral mucins in the respiratory mucosa, yet without toxicological significance.