Cyclosporine inhibits the activation of helper T cells that may be pathogenic in alopecia areata. Therefore we treated six patients with alopecia areata (five men, one woman) with oral cyclosporine, 6 mg/kg/day for 12 weeks. Three patients had alopecia universalis, one had alopecia totalis, and two had patchy alopecia areata of the scalp. Hair regrowth in the scalp of all patients occurred within the second and fourth weeks of therapy, followed by hair regrowth of the face and chest (in the male patients), pubic area, extremities, and axillae. Overall, the site of best response was the scalp. Cosmetically acceptable terminal hair regrowth on the scalp occurred in three of six patients. Significant hair loss, however, occurred in all patients within 3 months of discontinuation of cyclosporine treatment. Clinical response correlated with changes in immune cell infiltration of the hair follicles. The number of leukocytes per hair follicle was quantified in transverse scalp biopsy sections stained with a panel of monoclonal antibodies. The degree of terminal hair regrowth correlated significantly with decreases in follicular epithelial human lymphocyte antigen-DR and intercellular adhesion molecule-1 expression, T cells, helper/inducer (CD4) T cells, suppressor/cytotoxic (CD8) T cells and Langerhans cells (CD1+DR+) from the hair follicles during cyclosporine therapy. A significant decrease in the CD4/CD8 ratio occurred early in the course of treatment and was maintained throughout the therapy. This decrease suggests that cyclosporine not only cleared immune cells from the hair follicles but also altered the balance of regulatory lymphocytes.(ABSTRACT TRUNCATED AT 250 WORDS)