Methyl tert-butyl ether (MTBE) is the oxygenated gasoline additive most widely used in the U.S. to reduce the CO emission from motor vehicles. We developed a method using a high-temperature purge-and-trap procedure coupled with capillary gas chromatography-mass selective detection to determine MTBE and its metabolite, tert-butyl alcohol (TBA), in human urine. Several spiked-urine tests were conducted at different purging temperatures (25, 55, and 90 degrees C). The results indicated that the purging temperature affects the recovery of TBA from urine more than the recovery of MTBE. The mean recoveries of MTBE and TBA in the urine samples by the high temperature (90 degrees C) purge-and-trap gas chromatography-mass spectrometry method at different spike levels were 96.5+/-4.7% and 98.4+/-5.7%, respectively. The method was used to evaluate the urinary levels in a single subject exposed through inhalation to 1 ppm MTBE for 10 min in a controlled-environment facility. Increases in MTBE and TBA urinary excretion rates were clearly evident following the exposure to MTBE. Approximately 0.9% of the amount of MTBE inhaled was excreted unchanged as urinary MTBE, and 2.4% was excreted as urinary TBA within 10 h after exposure. The method developed is a simple, effective, sensitive, and reproducible procedure for evaluating human exposure to MTBE.