Methyl tert-butyl ether (MTBE) was first introduced in the U.S. as a synthetic gasoline additive in the 1970s. The uptake of MTBE by inhalation has been measured in exhaled breath under controlled conditions using integrated sampling techniques. Several studies, including some based on the analysis of exhaled breath, have demonstrated significant dermal absorption of chloroform and trichloroethylene while showering or bathing, and the dose is roughly comparable to that resulting from inhalation. Because of the dynamic equilibrium between the concentration of a volatile organic compound (VOC) in the blood and its concentration in exhaled breath,25 breath measurements can be used to estimate body burden and to detect changes in body burden with time. Most previous measurements of human breath concentrations of VOCs to determine the dose resulting from inhalation exposure to the pollutant in air have, however, relied on the use of integrated sampling methods and subsequent batch analysis. This has limited the number of samples that are typically collected in such exposure studies to about four during the uptake phase and usually no more than about twelve during the decay phase, thus reducing the reliability of data designed to address these issues. The purpose of the present study was to use the real-time breath measurement technology determine more precisely than previous studies the residence times in various physiological compartments for MTBE in blood and breath. The study was also designed to provide analogous on DBCM and on the blood/breath ratios for MTBE and DBCM. A secondary purpose was analyze the data in an attempt to develop a model for MTBE that allows for the inclusion of a mucous membrane component, if appropriate, since previous work has suggested that this may important component of MTBE distribution in the body.