The treatment of chronic severe asthma is unsatisfactory for many patients. The aim of the study was to determine the effects of treatment of steroid-dependent asthma with cyclosporin. We performed a double-blind, placebo-controlled, randomized, parallel group trial on the effect of cyclosporin on pulmonary function, asthma severity and tapering of prednisone in 34 steroid-dependent asthmatics (mean oral prednisone dose: 16 mg.day-1). The study consisted of: 1) baseline period (12 weeks); 2) experimental period divided into two parts: Part I (12 weeks) cyclosporin or placebo treatment; Part II (22 weeks) cyclosporin or placebo treatment and oral prednisone reduction; and 3) follow-up observation (8 weeks). Asthma symptoms score, pulmonary function tests (daily peak expiratory flow (PEF) and bi-weekly forced vital capacity (FVC), forced expiratory volume in one second (FEV1) and maximal mid-expiratory flow (MEF50), biochemical profile and blood cyclosporin levels were monitored throughout the study. Following cyclosporin administration, a slight beneficial effect on some subjective parameters of asthma severity was observed. At the same time, no beneficial effect on pulmonary function was noted. The time trends analysis of mean daily prednisone doses between the treatment groups revealed a statistically significant difference indicating that, during prednisone reduction, cyclosporin seemed to be slightly more efficient than placebo in reducing the requirement for systemic corticosteroid, even though the steroid reduction was accompanied by slight impairment of some pulmonary function. However, there was no significant difference in the final dose reduction between the treatment groups. These data and the known toxicity of the drug suggest a limited place for cyclosporin treatment in steroid-dependent bronchial asthma.