Concentrations of 15 VOCs including 1,3-butadiene, benzene, and styrene were measured in a wide range of urban microenvironments, viz: homes, offices, restaurants, pubs, department stores, coach and train stations, cinemas, libraries, laboratories, perfume shops, heavily trafficked roadside locations, buses, trains, and automobiles. For most target VOCs-including 1,3-butadiene and benzene-mean concentrations at heavily trafficked roadside locations were exceeded by those in automobiles and were comparable to those in pubs and train stations. With regard to indoor-outdoor relationships in homes, this study revealed higher mean indoor concentrations, no correlation between simultaneously measured indoor and outdoor concentrations, and significantly different patterns of diurnal variation. Thus-in poorly ventilated buildings-indoor emission source strength is considered a more significant influence on VOC concentrations than infiltration of outdoor air. In the six smoking homes studied, environmental tobacco smoke (ETS) was found to make a substantial contribution to concentrations of 1,3-butadiene. This finding was based on the significantly higher concentrations detected in smoking compared to nonsmoking homes, the significant correlation between 1,3-butadiene concentrations and those of 3-ethenylpyridine (an ETS marker), factor analysis, and the results of a source apportionment exercise based on ratios of 1,3-butadiene to 3-ethenylpyridine.