The differential pulse polarographic (DPP) behavior of chlorpyrifos (CP) was investigated over a wide range of pH (pH 1.8-pH 10.1). CP compound displays a well-resolved cathodic reduction peak at ¹1.2 V (vs. Ag/AgCl) (pH 3.2). This peak probably corresponds to the reduction of the --C=N-centre of the pyridyl moiety. The effect of solution and operational parameters on the sensitivity of the DPP peak was carefully examined in order to select the optimum conditions for determination of the CP compound. Under the optimum conditions the reduction response gives a linear calibration plot over a concentration range of 9.70 × 10 ¹7 -6.92 × 10 ¹6 M and the detection limit was found to be 8.7 × 10 ¹7 M. The effects of some diverse metal ions, anions and some other organophosphorus insecticides on the determination of CP compound were studied. The applicability of DPP for determination of the CP insecticide in a commercial sample as well as in some irrigation water (treated waste water and underground water) was detected.