This study investigated cytokine release by T-cell lines from atopic and nonatopic individuals in the presence of specific aeroallergen. Cell lines from atopic and nonatopic individuals secreted IL-2 for less than 14 and more than 21 days, respectively. All of the atopic, but not the nonatopic, cell lines exhibited a biphasic peak in IL-4 and IL-5 secretion. Flow cytometry revealed that, after 35 days, 89.3% of the atopic cells were T helpers and 73.2% were activated. Only 7.4% of the nonatopic cells displayed activation markers. In conclusion, T-cell differentiation may be controlled by other factors in addition to stimulation by aeroallergens.