A flow-injection conductimetric system procedure is proposed for the determination of paraoxon. The method is based on the inhibition of immobilized acetylcholinesterase in controlled porous glass beads (CPG) with acetylcholine as substrate. The enzymatic reaction is inhibited by a diethyl-p-nitrophenylphosphate (paraoxon) solution. A 1,1'-trimethylene-bis(4-formylpyridinium bromide)dioxime solution was used to reactivate the enzyme. The correlation between the peak height, for a given acetylcholine concentration, is linear from 1.0x10(-7) to 5.0x10(-5) mol l(-1) of paraoxon; therefore, the quantitative limit of detection was about 1.0x10(-7) mol l(-1) of paraoxon. For semi-quantitative purposes, the limit can be considered to be about 1.0x10(-8) mol l(-1). The relative estimated standard deviation obtained using a 1.0x10(-3) mol l(-1) acetylcholine solution and a 5.0x10(-6) mol l(-1) paraoxon solution was 2.2% (n=8).133423427