A simplified method is described for the determination of chlorophacinone, 2-[(p-chlorophenyl)-phenylacetyl]-1,3-indandione, in homogenized mice. Chlorophacinone is extracted with acetonitrile. After Florisil cleanup, the extract is injected into a high pressure liquid chromatograph for reverse phase chromatography on a polar Lichrosorb NH2 (10 micron) column, with a mobile phase of acetonitrile-water (80 + 20). An injection containing 70 ng chlorophacinone produces 1/2 scale peaks at 254 nm with a full scale absorbance of 0.1 unit, an order of magnitude improvement over the sensitivity reported earlier with a 280 nm detector. Six homogenized mice samples and six spiked homogenized mice samples were quantitatively analyzed for trace levels of chlorophacinone by this method. Recoveries from spiked samples, as determined by peak height measurement, were greater than 95%. Mean retention time for the chlorophacinone peaks in all samples was 6.05 +/- 0.05 min. Chlorophacinone levels determined in homogenized whole mouse samples ranged from 0 to 63 ppm.