The effects of IL-2, IL-3, and IL-4 activities on occurrence of allergic asthma induced by spores of mushroom have been studied by measuring the IL-2, IL-3, and IL-4 activities in culture supernatants of spleen lymphocytes from guinea pigs being stimulated with Con A. The IL-4 activity (14.9 +/- 0.18 u) in the culture supernatant was higher than control group (6.7 +/- 1.5 u). The IL-2 and IL-3 activities were all similar to that of the control group. The IL-4 synthesis was similarly raised as the IL-4 activity. These results indicated that there is a relationship between the occurrence of allergic asthma and the increase of IL-4.