In this prospective, double-sided patient-controlled therapeutical trial involving 20 patients with alopecia areata, we investigated the efficacy of topical acid dibutylester (SADBE) in the treatment of alopecia areata. Sensitisation was achieved with 2% SADBE in acetone followed by weekly application of topical SADBE to designated alopecia sites for 20 weeks. Untreated alopecia sites on the same patient acted as controls. Nineteen of the twenty patients completed 20 weeks of treatment. On the SADBE treated sites, excellent response (> 75% hair regrowth) was observed in 68% (13/19) of patients at the end of 20 weeks of treatment. On the untreated control sites, the corresponding figure was 11% (2/19). The difference in response between SADBE treated and untreated sites was statistically significant (P < 0.001). Mean onset of hair regrowth was 6 weeks after starting treatment. Patients with duration of alopecia 12 months or longer fared poorer compared with patients with a shorter duration of the disease. The extent of involvement did not appear to influence treatment outcome. Side effects were mainly local and were mainly local and were well tolerated. At 6 months follow-up, 33% (2/6) of responders with alopecia totalis relapsed compared to 11% (19) of those with patchy alopecia areata. We conclude that topical immunotherapy with SADBE is effective in inducing hair regrowth in alopecia areata.