Effects of administering technical Rabon® (2-chloro-1-(2,4,5-trichlorophenyl) vinyl dimethyl phosphate) at a concentration of 400 and 800 ppm in the feed of laying hens were investigated. The estimated mean daily intake of Rabon was 40.0 mg per hen for those receiving 400 ppm and 72.6 mg per hen for those receiving 800 ppm. Feeding of Rabon at 400 ppm resulted in excellent control of larvae of the house fly, Musca domestica L., Chrysomya megacephala (F.), and Parasarcophaga argyrostoma (Robineau-Desvoidy), but in poor control of Fannia pusio (Wiedemann). However, feeding of Rabon at 800 ppm resulted in good control of maggots of F. pusio . No hen mortality occurred that could be attributed to the insecticidal treatments, nor was there any inhibiting effect detected on blood plasma cholinesterase activity. Hens which received 800 ppm Rabon in their diet consumed less feed, produced fewer eggs, and did not maintain their body weight as well as the control birds. At 400 ppm, Rabon had less detrimental effect, and although birds at this concentration consumed less feed and produced fewer eggs than the control birds, they were able to maintain their body weight. Egg weight, interior egg quality, shell thickness, and odor were normal, but eggs from treated hens had a less desirable flavor than eggs laid by untreated hens. Feed efficiency was significantly less among both groups of hens receiving Rabon in the diet than among untreated control hens. A method was developed which used gas-liquid chromatography with a phosphorus-sensitive thermionic emission detector to determine Rabon ( cis ) and its low-melting isomer SD-13462 ( trans ). Eggs and tissues from hens slaughtered while on treatment and 7, 14, and 21 days after removal from treatment were analyzed for residues. The lower limit of detectability was 0.02 ppm. No detectable residues of Rabon or SD-13462 were found in the eggs or in any of the tissue samples except for two 800 ppm 11-day-posttreatment breast-muscle samples; two 800 ppm 0-day-posttreatment liver samples; three 800 ppm 0 day-posttreatment peritoneal-fat samples; and two 400 ppm 0 day-posttreatment fat samples. All but one (0.07 ppm) of the residues detected were in the 0.02 to 0.03 ppm range.