After informed consent was obtained and with the approval of the Local Ethical Committee, cyclosporine A (CsA) kinetics was studied in 63 psoriatic patients by giving them 2.5 mg/kg CsA orally. In order to calculate oral bioavailability, F, 22 patients were given the same dose i.v. Values of the calculated kinetic parameters were oral F = 22-63%; half-life, t1/2 beta, = 11.05-13.70 h; volume of distribution, Vd, = 4.00-5.02/L/kg; total body clearance, Cl, = 4.25-4.14 ml/min/kg. The area under the blood concentration time curve was more closely related to the dose (r = 0.66) than were trough levels (r = 0.52). No significant relationship was observed between the kinetic parameters studied and the age of the patient.