Environmental tobacco smoke (ETS) is one of the most common indoor pollutants to which many children are exposed. This study was set up to determine possible effects on cellular infiltrates in the nasal mucosa of children exposed to ETS. The research population consisted of a group of ten children exposed to more then 15 cigarettes/day and a control group of ten children without exposure. The groups were matched for age and gender. None of the children had an atopic constitution. Immunohistochemical staining techniques were used to determine the number of Langerhans cells, T cells, B cells, granulocytes, macrophages, mast cells and eosinophils in the nasal mucosa. IgE+ cells and eosinophils were seen in significantly higher cell numbers in the nasal mucosa of children exposed to ETS (Mann-Whitney U-test). IgE+ mast cells were not found to be more numerous in the ETS-exposed group. We can conclude that exposure to ETS causes changes in cellular infiltrates which partly resemble those seen in the nasal mucosa of allergic children. However, no sign of allergic sensitisation can be found in the nasal mucosa. Children with a genetic predisposition to allergic disease will probably suffer most from the 'unstable' nasal mucosa due to ETS.