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Routine monitoring of cyclosporine and tacrolimus levels is necessary to minimize adverse side effects and to ensure effective immunosuppression. The RXL Dimension apparatus conceived for ACMIA technologies is proposed to determine C0 and C2 cyclosporine levels and also tacrolimus levels in whole blood without any dilution or pretreatment using specific calibrators and Flex reagent cartridges (reagent stability: 72 hours for Neoral C0 and C2; 48 hours for tacrolimus). The assay ranges were between 25 to 500 ng/mL for C0; 350 to 2000 ng/mL for C2; and 1.2 to 30 ng/mL for tacrolimus. Within-run and between-day imprecision were <10% for cyclosporine. The coefficient of linearity was r(2) = .998 for C0, C2, and tacrolimus. Moreover, for cyclosporine and tacrolimus assays, the time for the first result was 20 minutes. Cyclosporine (C0, n = 152; C2, n = 54) and tacrolimus (n = 70) ACMIA assays were compared with enzyme-multiplied immunoassay technique (EMIT) cyclosporine and tacrolimus assays (V-Twin, Siemens ex-Dade Behring Laboratories) among 276 transplant patients: 119 kidney, 67 liver, 28 heart, and 62 bone marrow transplantations. Values obtained with the ACMIA assay were highly correlated with the EMIT assay for CsA C0 levels (ACMIA = 1.04 EMIT - 9.32; r(2) = .97); CsA C2 levels (ACMIA = 1.15 EMIT - 53.7; r(2) = .94); and tacrolimus levels (ACMIA = 0.93 EMIT - 0.16; r(2) = .93). In conclusion, the RXL Dimension analyzer is a useful tool for routine monitoring with a single method for C0 and C2 cyclosporine and tacrolimus level determinations in whole blood without any dilution or preanalytic treatment.