The distribution of cyclosporin A (CsA) in the blood, saliva, tears, aqueous humour, vitreous, and cerebrospinal fluid has been studied after oral treatment with 5 mg/kg/day of CsA or application of 2% CsA eye drops in olive oil solution. After oral treatment all patients had high CsA levels in blood. Measurable levels of CsA were also found in the saliva and tears. Patients without any intraocular inflammation or patients with mild uveitis did not have any detectable CsA in the aqueous humour. However, patients with severe uveitis had significant levels of CsA in the aqueous humour and in the vitreous. No CsA was found in the cerebrospinal fluid of two patients with central nervous system manifestations of Behçet's disease. After local treatment with 2% CsA eye drops no detectable levels of CsA were found in the blood, the saliva, the aqueous humour, or the vitreous even in patients with severe uveitis.