A 33-year-old patient suffered from recurring Beh,cet's colitis despite treatment with corticosteroids and later cyclosporin. The patient was then successfully shifted from cyclosporin, a T-cell specific immunosuppressant, to fusidic acid treatment (500 mg t.i.d.). During fusidic acid treatment, he went into complete remission, and his prednisolone dose could be reduced from 30 to 5 mg/day. The case report substantiates recent in vitro data indicating that fusidic acid has a similar effect on T-cell function as cyclosporin. It is suggested that the effect of fusidic acid in other chronic immunoinflammatory diseases should be examined.