A monoclonal antibody against CD-1(T6) was used for studies in the nasal mucosa of patients with isolated grass-pollen allergy to determine whether the number of CD-1-positive cells, presumably Langerhans cells, depends on the season in which the nasal biopsy is performed. An earlier study had demonstrated that during the grass-pollen season, there are significantly more CD-1-positive cells in nasal mucosa of patients with isolated grass-pollen allergy than in nonallergic control subjects without nasal complaints. During the grass-pollen season, the nasal epithelium of patients with an isolated grass-pollen allergy demonstrated significantly more CD-1-positive cells than before and after the season. Before and after the season, the number of CD-1-positive cells in epithelium of the allergic patients was not significantly greater than the corresponding number in epithelium of nonallergic subjects without nasal complaints.