The effect of systemic recombinant interferon alpha-2a (rIFN-alpha-2a) on the mucocutaneous lesions in Adamantiades-Behçet's disease was assessed in ten patients with the mucocutaneous type of the disease. rIFN-alpha-2a was applied subcutaneously at a dose of 9 x 10(6) IU three times a week for 6 months. Five patients showed a significant reduction in the number, severity, duration and frequency of their mucocutaneous lesions during the treatment compared with the pretreatment phase, whereas in two patients a complete remission and in three patients a partial remission was achieved. In two patients, one with complete and one with partial remission, recurrence of the cutaneous symptoms occurred shortly after discontinuation of the treatment. Renewed administration of rIFN-alpha-2a again led to remission of the symptoms. In another patient with initial partial remission followed by exacerbation, interferon alpha antibodies were detected and the patient responded again when 15 x 10(6) IU rIFN-alpha-2a was administered three times a week. Three patients did not show any change in the characteristics of their lesions, while two patients experienced progression of their disease during treatment. Side-effects were generally mild and well tolerated, but the treatment was discontinued earlier than planned in one patient because of fatigue, myalgia, hypotonus and diarrhoea. Since the classical treatments are generally unsatisfactory, the results of the present study justify the administration of systemic rIFN-alpha-2a in the treatment of the mucocutaneous type of Adamantiades-Behçet's disease.