A 17-year-old female presented with alopecia universalis, which appeared following widespread eczematous dermatitis. An immunohistochemical study demonstrated that CD8(+) T cells infiltrated into hair follicles with satellite cell necrosis of keratinocytes. The precedence of the autosensitization dermatitis suggested that T cells concerned with the eczematous reaction also attacked hair follicles, or alternatively, that those T cells sequentially activated another population of cytotoxic T cells. We found that she had a continuously low level of serum IgE (<1 units/ml), and this abnormality urged us to investigate interleukin (IL)-4 production of T cells. Although the patient had a normal number of CD4(+) T cells, the production of IL-4, but not IL-10, was profoundly impaired as assessed by a reverse transcriptase polymerase chain reaction analysis, suggesting the possible relationship between the baldness and IL-4 reduction. The autoimmune hair loss might occur via activation of cytotoxic T cells and Th(1) cells as a result of a relief from IL-4 control.