The food sample extract is cleaned up on a Florisil column and the 6% ethyl ether in petroleum ether cluate is subjected to repeated concentrations, using a micro-Snyder column, to expel volatile materials that absorb ultraviolet (UV) light. The sample and standard solutions of heptachlor and heptachlor epoxide are placed in quartz cells and exposed to UV radiation in the dark. Characteristic photoderivatives of the respective pesticides which form in the sample extract are identified and measured by comparison with those formed in the irradiated standard solutions, using electron capture gas-liquid chromatography. Recoveries of the 2 pesticides from 13 products, fortified at levels from 0.01 to 0.3 ppm and determined after derivatization, ranged from 67 to 110%.