Polished rice grains were fortified with 500 ppb of chlorpyrifos. The fortified residues were analyzed by gas chromatography with a nitrogen-phosphorus detector or a Hall detector. Chlorpyrifos and its breakdown product 3,5,6-trichloro-2-pyridinol were recovered from fortified rice grains in the levels of 456 and 3.4 ppb, respectively. Washing rice grains with water removed approximately 60% of the chlorpyrifos residues. Fortified chlorpyrifos was found in cooked rice at a level of 130 ppb, which was approximately 30% of the original quantity. Acid treatment was required to remove chlorpyrifos bound to proteins or carbohydrates in the cooked rice