Considered a wide range of indoor and outdoor urban microenvironments in a study of the concentrations of 15 volatile organic compounds. For most VOCs, mean concentrations in cars exceeded those at heavily trafficked roadside locations. No correlation was found between indoors and outdoors, though concentrations were higher indoors. As a consequence, in poorly ventilated buildings, indoor emission source strength is considered a more significant influence on concentrations of VOCs in indoor air than outdoor air concentrations. Six of the homes studied were smoking homes, and here it was found that environmental tobacco smoke made a substantial contribution to concentrations of 1,3-butadiene.