An amperometric immunoassay was developed by coupling the enzyme-linked immunosorbent assay (ELISA) microtiterplatesystem with a polyaniline-perfluorosulfonated ionomer composite (PA/NF) electrode incorporated flowinjection analysis(FIA) system and used for the analysis of Tal 1 protein, found in leukemic T cell. Rabbit polyclonal antibody (pAb) against Tal1 and urease–pAb were used, respectively as the captured protein and enzyme labeled conjugate for sandwich immunoassay ofTal 1. Characteristics of the PA/NF electrode such as reproducibility, stability and sensitivity were studied. The detection limitsof the PA/NF electrode for NH4+ and urease were found to be 5_M and 0.05 nM, respectively. Assay conditions such as theamount of pAb needed for coating the plate, the concentration of urease–pAb conjugate appropriate for the immunoreactionand the incubation time for urea to react with the bound urease–pAb in the microtiter-wells were also studied. A detectionlimit as lower as 0.5 ng/ml and a dynamic range of 1.0-100 ng/ml were found for the immunoassay of Tal 1 protein with thedeveloped immunoassay system.