A competitive continuous immunoassay system for the determination of 3,5,6-trichloro-2-pyridinol (TCP), the major degradation product of the insecticide chlorpyrifos, in water is described. The immunoassay system is based on the transient retention of the specific LIB-MC2 monoclonal antibody anti-TCP as a biotinylated derivative using the streptavidin-biotin interaction. The permanent immobilization of streptavidin on controlled-pore-glass provides an adequate active support for the transient retention of the biotinylated monoclonal antibody anti-TCP. In a subsequent step, the immuno-competitive reaction between the biotinylated LIB-MC2 and the TCP/hapten-POD mixture takes place. This competitive assay relies on the determination of the biocatalytic action of peroxidase, retained in the active support, on a derivatization reaction which yields a fluorescent product. The method exhibits a determination range of 0.01-200 microg L(-1) of TCP (r2=0.9919, n=9) with a precision, expressed as RSD, lower than 4.2% and a sampling frequency of 3 h(-1). The approach has been applied to the determination of TCP in water with recoveries of 89.7-105.6%.