The effect of processing on residues of chlorpyrifos in rice and corn was determined. Chlorpyrifos solution (0.1%) sprayed on jute sacks containing corn resulted in absorption of residues in kernel and cob up to six months. A similar trend was observed in rice. Radiotracer studies revealed very low levels of bound residues (0.2-0.8 mg/kg) present in rice only. The usual practice of washing rice and corn before cooking reduced chlorpyrifos residues by as much as 57% to 100%. Residues in wash water declined with each washing. Cooking further reduced the residues of chlorpyrifos only when volatilization was possible. Chlorpyrifos appeared to be presistent. Cooking rice in a pot with the lid on did not produce any substantial reduction in the chlorpyrifos content. The practice of storing rice and corn in the Philippines does not give rise to chlorpyrifos residues which may exceed the recommended daily intake of 0.01 mg/kg-bw.