N,N-Diethyl-m-toluamide (DEET) is an effective component of several insect repellent products. A 19-year-old woman was admitted to the emergency department following ingestion of 15-25 mL 95% diethyltoluamide (Muscol). Serum and urine toxicology screening tests were negative except for detection of DEET. DEET was qualitatively identified and quantitated by gas chromatography-mass spectrometry. Concentrations of DEET based on selected ion monitoring (ion at m/z 119) were 63.0, 17.2, 1.9, and less than 0.2 mg/L in serum specimens collected at 2, 5, 24, and 48 h following ingestion, respectively. Serial monitoring of DEET concentrations and the cardiac abnormalities observed in this case following oral ingestion were not reported previously.