Although infiltrating lymphocytes in the lesion of alopecia areata are considered to play an important role in the pathogenesis, specific functions of these lymphocytes in the disease have been rarely studied.We studied spontaneous expression of IL-4 and IFN-γ mRNA in peripheral blood mononuclear cells, which might reflect characteristics of lymphocytes in the lesional skin, from eighteen patients and eight healthy individuals using semi-quantitative RT-PCR method. Amplification signals for IL-4 were slightly higher, while those for IFN-γ were slightly lower in the patients than in healthy controls. Among the patients, the intensities of amplification signals for either IL-4 or IFN-γ in those with severe symptoms were much stronger than those with mild symptoms. These results suggested that lymphocytes in the patients with severe symptoms were activated in vivo. Besides, different levels of the expression of IL-4 and IFN-γ mRNA, Th2 and Th1 cytokine respectively, in the severe condition, suggested the heterogeneous pathogenesis of alopecia areata.