Allergic asthma caused by mushroom spores (Pleurotus sapidus besidiospores) is a common health problem among mushroom-cultivating workers in China. An animal model of allergic asthma through the challenge of Pleurotus sapidus besidiospores in primed rats was developed for investigating the role of cytokines in the pathogenesis of the disease. In the study a series of related cytokines and their receptors, including their activity and mRNA levels of spleen lymphocytes isolated from asthmatic rats, were measured. Determined by 3H-TdR incorporation assay and NAG microcolorimetric assay, Con A-induced spleen lymphocyte proliferation and IL-2 activity in culture supernatants of spleen lymphocytes from 7-day challengedrats with allergic asthma increased significantly by 261% and 208%, respectively, as compared with those in the control. Cytokines and their receptor expression at mRNA levels were determined by RNA/cDNA hybridization, using (α-32P-dCTP radiolabeled cDNA probes for different cytokines and their receptors in vitro. The results showed that mRNA expression of IL-4, GM-CSF, IL-6, IL-2 and IL-2R, except IL-6R, in lymphocytes of 7-day-challenged asthma-suffering rats, increased significantly by 54%, 45%, 170%, 83% and 76%, respectively. In 2-day challenged-rats, mRNA levels of IL-4, IL-6 and IL-2 increased by 37%,58% and 125%, respectively, whereas mRNA leve1s of GM-CSF, IL-2R and IL-6R remained unchanged. Thus, the experimental results suggested a significant increase in TH2type cytokines in the pathogenesis of Pleurotus sapidus besidiospore-induced allergic asthma and IL-4 may play an essential role.