Abstract The immunohistology of the nasal mucosa was examined in 13 grass pollen—sensitive patients and in seven normal nonatopic control subjects before and during the pollen season. Cryostat sections (6 μm) of biopsy specimens from the inferior turbinate were immunostained with the alkaline-phosphatase antialkaline-phosphatase method and a panel of monoclonal antibodies. Mast cell subtypes were measured with a double sequential immunostaining method. Within the submucosa, seasonal increases in total (MBP +, p < 0.01) and “activated” (EG2 +, p < 0.01) eosinophils were observed for the patients, which were significant when these counts were compared with counts for those of control subjects (MBP + p < 0.01; EG2 + p < 0.001). Within the nasal epithelium, seasonal increases in total ( p < 0.05) and “activated” ( p < 0.02) eosinophils were also observed. Mast cell counts revealed seasonal increases in tryptase-only positive mast cell (MC T) ( p < 0.02) but not chymase plus tryptase—positive mast cells (MC TC) within the epithelium that were significant when counts were compared with those of control subjects ( p < 0.03). No significant changes were observed within the submucosa or epithelium for total leukocytes (CD45 + cells) or T-lymphocytes (CD3 +, CD4 +, CD8 +, and CD 25 + cells) for either group. Similarly, no significant changes were observed for neutrophils (antielastase), macrophages (CD68 +), nor HLA-DR + cells. In the subjects with rhinitis, seasonal submucosal CD3 + counts correlated with MBP + eosinophils ( r = 0.56; p < 0.05) and MC TS ( r = 0.65; p < 0.02). Similarly, seasonal epithelial EG2 + eosinophil counts correlated with MC Ts ( r = 0.56; p < 0.05). The results indicate that seasonal allergic rhinitis is associated with local accumulation of “activated” eosinophils and the epithelial migration of MC Ts but not MC Ts during natural grass-pollen exposure.