Abstract: A method of liquid-phase enzyme-immunoassay for thyroxine in human serum is presented.T₄-alkaline phosphatase conjugates were used as the tracer.In this method blood samples are extracted with ethanol to liberate T₄.Second antibody was used as the separating reagent.P-nitrophenyl phosphate was used as substrate.The method is simple to handle and sensitivity,accuracy and precision are the main features sufficient enough to meet the clinical demand.The least detectable amount for T₄ was 12.5ng/ ml.The recovery rate is 99.7%.The variation coefficients of intraassay and interassay are 50% and 6.7% respectively.