Immunological mechanisms have long been suggested to mediate hair loss in alopecia areata. In this process hair bulb melanocytes and dermal papilla fibroblasts are believed to be primarily involved. In the present study we further investigated the role of humoral factors in alopecia areata. Three different experiments were performed on normal human epidermal melanocytes as well as normal human dermal fibroblasts: (i) incubation with medium containing 2, 10, or 20% alopecia areata serum (n = 12 patients) for 16 h, (ii) incubation with medium supplemented with preheated alopecia areata serum (1 h at 56 degrees C) and healthy human fresh serum as a complement source (1:1) and (iii) incubation with 2, 10 or 20% alopecia areata serum but, in addition, containing peripheral blood mononuclear cells from healthy subjects (effector/target ratio, 50:1). As controls, normal human fibroblasts and normal human epidermal melanocyte cultures were also incubated with serum from healthy individuals (n = 5) under the same culture conditions. The results showed that alopecia areata serum exerted a significant stimulation of proliferation of both normal human fibroblasts (p > 0.05 at 2%, p > 0.05 at 10%, p < 0.05 at 20%), and normal human epidermal melanocytes (p > 0.05 at 2%, p < 0.05 at 10%, p > 0.05 at 20%).(ABSTRACT TRUNCATED AT 250 WORDS)