Volatile organic compounds (VOCs) and other air pollutants, including several toxic compounds, are present at high levels in garages and can transferred into residences with attached garages or other buildings where they may constitute a significant exposure source. However, there is little information in the literature regarding either pollutant levels in garage environments or the significance of residential garages as air pollution sources affecting indoor air quality and exposure. In this study, multi-component perfluorocarbon tracer (PFT) gas techniques are used to examine air exchange rates (AERs) and air flows between houses and their attached garages, and passive samplers using thermally-desorbable adsorbents analyzed by GC-MS are used to quantify a wide range of VOC species. A total of 15 single family houses located in suburban sites in southeast Michigan, USA, were studied during a generally cool spring season. Each house, which was smoker-free, underwent an inspection to determine possible VOC sources, and a resident questionnaire was used to record activities that might influence measurements. Multiple PFT sources and VOC samplers were deployed in each house, garage, and outdoors simultaneously for a 4-day period. The effective AERs across the 15 houses averaged 0.41 ± 0.35 hr−1, and AERs across the 15 garages averaged 0.77± 0.51 hr−1. Air flows from the garage to the house averaged 6.5 ± 5.3% of the houses' overall AER. The reverse flow, from the house to the garage, was lower in most cases. A total of 39 VOC species were detected indoors, 36 in the garage, and 20 in ambient air. High concentrations of gasoline-related VOCs were found in most but not all of the garages, e.g., benzene averaged 37 ± 39 μg m−3. Concentration profiles matched evaporated gasoline; paints, solvents and oils were also indicated. Indoor concentrations of gasoline components were highly correlated with garage-to-air flows, indicating that nearly all of the benzene (and other VOCs) in the houses were attributed to garage sources. Concentrations and air flows showed significant variability, e.g., the highest benzene concentrations were 160 and 8 μg m−3 in garages and residences, respectively, and the highest garage-to-house air flow was 20% of the houses' total AER. This study demonstrates the significance of attached garages as a major source of VOC exposure. VOC exposures may be reduced by reducing emissions and concentrations in garages, and by tightening the garage-to-house barrier.