Objective        To prepare a polyclonal antibody (mAb) against huma

n triiodothyronine (T

3

) and to establish a new method of non-equilibrium competitive chemiluminescence immunoassay (CLIA) with FITC system for clinical determination of serum free triiodothyronine (FT

3

).       Methods        Polyclonal antibody of T

3

was prepared by immunizing New Zealand rabbits with human T

3

-bovine serum albumin (BSA)

purified by affinity chromatography

and labeled with horse radish peroxidase (HRP). FITC was conjugated to T

3

-analogue

and microwell was coated by anti-FITC antibody. FITC-T

3

analogue would combine to anti-FITC antibody to form solid phase T

3

-analogue on microwell. FT

3

if existed in sample

would combine to T

3

antibody-HRP and compete with solid phase T

3

-analogue. The amount of the complex would be measured through enzymatic chemiluminescence immunoassay reaction. Compared with those of the method coating by T

3

-bovine serum gamma globulin (BGG) (non-FITC system)

the sensitivity

precision

stability and clinic correlation of this method were evaluated. This method as well as Roche Elecsys 2010 System was used in 120 clinical serum samples for FT

3

determination.       Results       ELISA showed the prepared antibody had a high specificity to T

3

. The linear range and sensitivity of human serum FT

3

detected by chemiluminescence immunoassay with FITC system were 0.25 to 50 pg/ml (R0.99) and 0.25 pg/ml

respectively

and the coefficients of variability within and among batches were all under 5％

and these results were better than those of the non-FITC system. The results obtained from chemiluminescence immunoassay with FITC system were correlated with those of the Elecsys 2010 system

and the correlation coefficient was 0.962 2.       Conclusion        The antibody against human T

3

with high purity and specificity is successfully prepared. The quantitative diagnostic kit for FT

3

by non-equilibrium competitiv

e chemiluminescence immunoassay using FITC system provides a rapid

sensitive and accurate determination of FT

3

and is suitable for clinical diagnosis.