Asian sand dust (ASD) contains microbial materials, sulfate (SO(4)(2-)), and nitrate (NO(3)(-)), and is derived from air pollutants in East China. ASD reportedly causes adverse respiratory health effects; a case in point is aggravated allergen-associated experimental lung eosinophilia. Guinea pigs were administered normal saline (control), ASD (0.3 mg/animal), ASD (0.6 mg/animal), Japanese cedar pollen (JCP) (0.2 mg/kg body weight), JCP + ASD (0.3 mg/animal), or JCP + ASD (0.6 mg/animal), into their nasal cavities at seven weekly intervals. The number of sneezes, amount of nasal secretions, and nasal obstructing response were measured as indices of nasal responses. Total immunoglobulin E (IgE) antibodies in serum and the number of eosinophils, histamine, and arachidonic acid metabolites in nasal cavity lavage fluids (NCLF) were also measured. ASD enhanced the JCP-associated nasal obstructing response, but not the number of sneezes or amount of nasal secretions. ASD enhanced JCP-associated cysteinyl leukotrienes (C(4), D(4), E(4)) and histamine production in NCLF. ASD augmented the number of eosinophils in NCLF and total IgE in serum induced by JCP. ASD enhanced eosinophil recruitment in the nasal mucosa, and goblet cell proliferation in the nasal epithelium induced by JCP. These results suggest that ASD enhances the nasal allergic reaction induced by repeated JCP administration in guinea pigs.