Ethyl tert-butyl ether (ETBE) might replace methyl tert-butyl ether (MTBE), a widely used additive in unleaded gasoline. The aim of this study was to evaluate uptake and disposition of ETBE, and eight healthy male volunteers were exposed to ETBE vapor (0, 5, 25, and 50 ppm) during 2 h of light physical exercise. ETBE and the proposed metabolites tert-butyl alcohol (TBA) and acetone were analyzed in exhaled air, blood, and urine. Compared to a previous MTBE study (A. Nihlen et al., 1998b, Toxicol. Appl. Pharmacol. 148, 274-280) lower respiratory uptake of ETBE (32-34%) was seen as well as a slightly higher respiratory exhalation (45-50% of absorbed ETBE). The kinetic profile of ETBE could be described by four phases in blood (average half-times of 2 min, 18 min, 1.7 h, and 28 h) and two phases in urine (8 min and 8.6 h). Postexposure half-times of TBA in blood and urine were on average 12 and 8 h, respectively. The 48-h pulmonary excretion of TBA accounted for 1.4-3.8% of the absorbed ETBE, on an equimolar basis. Urinary excretion of ETBE and TBA was low, below 1% of the ETBE uptake, indicating further metabolism of TBA or other routes of metabolism and elimination. The kinetics of ETBE and TBA were linear up to 50 ppm. Based upon blood profile, levels in blood and urine, and kinetic profile we suggest that TBA is a more appropriate biomarker for ETBE than the parent ether itself. The acetone level in blood was higher after ETBE exposures compared to control exposure, and acetone is probably partly formed from ETBE.