Modifications to an earlier procedure for chlorophenoxyacetic acid residues are introduced to provide better recoveries, cleaner samples, and sensitivities down to 0.02 ppm. These changes include (1) extracting with acetonitrile or CHCI3, (2) more effective methylation of the acids, (3) Florisil chromatography to separate PCP from the other herbicides, and (4) isothermal gas chromatography by electron capture or microcoulometric detection. The improved procedure was compared with the previous one, using several total diet composites at fortification levels of 0.01–0.05 ppm. Results showed that usable chromatograms were obtainable only with the improved procedure. Recovery studies were made on all commodity groups except for fats, oils, and shortenings. Microcoulometric results were good. Compounds studied were MCP, 2,4-D, 2,4,5-T, 2,4,5-TP, 2,4-DB, PCP, and 2,3,6-TBA.