An analytical gas/liquid chromatographic (GLC) protocol is described for the quantitation of pemoline in biological fluids of the horse. Plasma samples containing known quantities of pemoline and its analog as an internal standard (IS) were deproteinized with 5-sulfosalicylic acid, heated at 80 degree C, and centrifuged. 5-Phenyl-2,4-oxazolidinedione, the hydrolytic product of pemoline in acid medium, was extracted with dichloromethane (DCM). The organic layer was in turn re-extracted with 1% NaHCO3. The aqueous layer was acidified with HCI, and re-extracted with DCM, which was evaporated to dryness. The resulting residue was methylated with ethereal diazomethane. The methylated dione was dissolved in benzene, and analyzed with a gas/liquid chromatograph equipped with a tritiated scandium foil (Sc3H) electron capture detector (ECD). Urine samples to which pemoline was added were hydrolyzed with hydrochloric acid and carried through the analytical procedure in a manner similar to the plasma, except that the urine was further washed with lead acetate solution prior to the sodium bicarbonate extraction. The lower limits of detection were found to be 0.05 microgram/ml for plasma and 0.1 microgram/ml for urine when 1.0 ml of sample was used. This procedure can be used for pemoline detection control in international sporting events.