Tacrolimus (FK506, Prograf) is a potent macrolide immunosuppressant used for prevention of organ transplant rejection following transplantation. It has been clear for many years that, as a drug with a low therapeutic index and high inter-and intrapatients pharmacokinetic variability, it requires individualized monitoring of blood concentration. Several methods have been developed to monitor tacrolimus; immunoassays, bioassays and LCMSMS. The purpose of this study was to develop application for the EMIT Tacrolimus assay on the Hitachi 902 analyzer. Application protocol on this analyzer is nonexistent. We optimize the programm chemistry parameters to arrive at the following assay characteristics on the Hitachi 902. Assay results were linearly related to the concentration for the wide range which was examinated (0 - 40 ng/mL). We report the precision, accuracy, linearity, sensitivity of this assay. The CV was less than 10%. Calibration stability is at least 21 days. The reagent cartridge in the instrument is stable 2 months between runs. However, specimens from 87 kidney transplant patients were analyzed and results were compared to those from the Abbott MEIA II assay on IMx analyzer. Correlation between the methods was good (r = 0,961). This application for the EMIT 2000 Tacrolimus assay on the Hitachi 902 analyzer enhances the versatility of the immunoassay for routine therapeutic drug monitoring of this immunosuppressant in the clinical setting.