A fluorescence polarization immunoassay (FPIA) for cyclosporine A (CsA) determination in blood was evaluated. The method demonstrated a good reproducibility both in within-run and between-run assays. The linearity range was 35-990 micrograms/L. Comparison of measurements in patients' whole blood with radioimmunoassay results showed higher estimates by the FPIA despite the good correlation coefficient. Finally, a poor agreement was observed between the evaluated method and the high-performance liquid chromatographic technique for CsA determination.