A simple, sensitive, and specific gas chromatographic method for the quantitation of 4-methylpyrazole in plasma and urine is described. Samples containing 4-methylpyrazole, with 3-methylpyrazole as the internal standard, are extracted into ether and the concentrated ethereal extracts are chromatographed on a Carbowax 20M column using nitrogen-selective detection. Standard curves are linear and reproducible over the range of 25-1000 ng/mL for plasma and 0.5-5 micrograms/mL for urine. Recovery of 4-methylpyrazole is complete from plasma and urine, and the overall between-day coefficient of variation is within 6.0%. No interference is observed from the extractive constituents of plasma and urine. The assay method is suitable for an examination of 4-methylpyrazole disposition in animals and humans.