Background: Eye involvement is the main cause of morbidity in Behcet's syndrome. The efficacy of the combined use of azathioprine and interferon alfa in treating this condition has not been studied. Methods: Ten male BD patients with retinal involvement but no irreversible structural changes were treated with azathioprine 2.5 mg/kg/day and IFNalpha2b three times weekly for 24 weeks in an open trial. At week 24, IFNalpha was stopped and the patients continued to use azathioprine or received other immunosuppressives as indicated. Clinical response was assessed by visual acuity changes of either eye under the combination treatment and during the follow-up after stopping interferon. Results: As compared to the study entry, the mean visual acuities of either eye increased significantly at the end of the combination treatment (right eye 5.8 +/- 1.26 vs, 8.3 1.14, P = 0.043, left eye 6.3 1.15 SEM vs. 9.1 +/- 0.9 SEM; P = 0.027). The improvement in visual acuity persisted in the nine patients who were followed for 7.2 +/- 1.6 SEM months after stopping interferon. Reversible hematologic toxicity, mostly in the form of leukopenia, was detected in six patients during the combination treatment. Conclusions: The combination of IFNalpha and azathioprine appears to be effective for eye involvement of DB. However, the frequency occurrence of myelosuppression mandates close monitoring.