Alopecia areata (AA) is a relatively common reversible hair loss disorder usually manifesting as patchy areas of complete hair loss on the scalp and other body parts that can progress to complete loss of all body hair. This condition is now generally assumed to be an autoimmune disease with the hair follicle (HF) as the principal target tissue. AA may be passively transferred by T cells and there is some evidence that serum IgG may also disturb hair cycling. Here, we examine whether the status of anti-HF antibody reactivity is altered during hair regrowth associated with topical immunotherapy using the contact sensitizer diphencyprone. Eleven patients with severe AA of the scalp were treated with diphencyprone on one side of the scalp and serum was obtained from each patient before the start of therapy, after unilateral hair regrowth, during continuing hair regrowth and in some cases after complete and sustained regrowth. The presence and titer of circulating antibodies to HF was assessed by indirect immunofluorescence and immunoblotting analysis. A striking reduction was detected in both the titer and range of HF components/antigens targeted by anti-hair follicle IgG antibodies in those patients that exhibited complete and sustained hair regrowth after DCP-treatment. By contrast, unilateral hair regrowth was associated with no change, or even an increase, in anti-HF antibody titer and reactivity. Therefore we can conclude that the down-regulation of antibody reactivity is likely to be a result rather than the cause of hair regrowth induction by topical immunotherapy. As this immunotherapy is associated with a reduction in the titer/pattern of anti-HF antibodies, these may hold the key to the identity of the HF antigen targets in AA. Moreover, the presence/titer of anti-HF antibodies may be a marker of clinical disease activity or opportunity for spontaneous regrowth.