Twelve subjects living in houses with levels of airborne glucan of at least 4 ng/m³ (G+) and six subject living in houses with levels of airborne glucan of less than 1 ng/m3 (G0), were exposed to grifolan suspended in saline as well as to saline alone. Spirometry, methacholine challenge and blood sampling were performed before, immediately after and 24 h after exposure. There was no difference between the groups comparing spirometry or airway responsiveness, neither before the two exposures or thereafter. Comparing the groups before exposure showed that they differed regarding the number of cytotoxic T cells in the blood (CD8+S6F1strong). The G0 group had a higher ratio of cytotoxic/noncytotoxic T cells compared to G+, which might be interpreted as an increased trapping of cytotoxic cells in the lung tissue in subjects living in homes with glucan exposure. Blood mononuclear cells from G+ also showed an increased production of TNF in in vitro non stimulated cells compared to cells from G0. After exposure to saline, the non stimulated TNF production was increased in the G0 group while exposure to (1->3)-b-D-glucan resulted in an increase in both groups. An increase in the number of blood neutrophils and serum levels of myeloperoxidase was shown in both groups after both types of exposure.