An analytical procedure is described for determining residues of rotenone, rotenolone, dehydrotenone, and rotenone in admixture in animal chow and tissues. The methanol or ethyl ether extracts from samples of chow and tissues, respectively, are subjected to a liquid-liquid partitioning cleanup with hexane-acetonitrile, further cleanup on a column of silica gel, and subsequent analysis by high pressure liquid chromatography using an ultraviolet absorption detector set at 295 nm. Animal chow, mouse fetuses, and gastrointestinal tracts spiked with 0.5 ppm of each compound in admixture yielded average recoveries of 92, 51, and 79%, respectively; minimum quantities of the 4 compounds detectable in the 3 substrates averaged 0.12, 0.04, ajd 0.14 ppm, respectively. Stability studies indicate that rotenone reacts with animal chow with a half-life of 7--8 days and is photodegraded in incandescent light with a half-life of 0.65 day. No transplacental transfer of rotenone or its products was observed in fetuses from mice receiving 7 consecutive daily doses of rotenone at levels up to 25 mg/kg.