In a few patients with chronic sarcoidosis, prolonged, unacceptably high doses of corticosteroids are required to achieve symptomatic relief. In these cases, a corticosteroid-sparing drug might be administered to allow long-term treatment without the adverse effects of corticosteroids. This study examines azathioprine as a prednisolone-sparing treatment. In an open study, the course of 11 patients with chronic sarcoidosis was analysed. In an induction phase, 2 mg azathioprine x kg body weight (BW)(-1) x day(-1) in combination with 0.6-0.8 mg prednisolone x kg BW(-1) x day(-1) were administered with prednisolone being reduced to 0.1 mg x kg BW(-1) x day(-1) within 2-3 months. This was followed by a 21-22-month maintenance phase with 2 mg azathioprine x kg BW(-1) x day(-1) and 0.1 mg prednisolone x kg BW(-1) day(-1). Clinical parameters and immunological findings of bronchoalveolar lavage (BAL) were analysed. All patients had significant symptomatic relief and improvements or resolutions of physiological, serological and radiographic findings without suffering from serious adverse effects. Nine of 11 patients completed therapy after 19-26 months, and 2/11 patients terminated therapy after 8 and 12 months, respectively. Eight patients had remissions lasting 4-73 months. Three relapses occurred after 8, 18, and 22 months. During the induction phase, BAL cell composition changed and their activity in terms of cytokine release was suppressed. This preliminary study suggests that azathioprine may be effective as a corticosteroid-sparing agent in long-term therapy of sarcoidosis, but a much larger study is necessary to give the definitive answer.