Personal exposures and breath concentrations of approximately 20 volatile organics were measured for 200 smokers and 322 nonsmokers in New Jersey and California. Smokers displayed significantly elevated breath levels of benzene, styrene, ethylbenzene, m + p-xylene, o-xylene, and octane. Significant increases in breath concentration with number of cigarettes smoked were noted for the first four aromatic compounds. Based on direct measurements of benzene in mainstream cigarette smoke, it is calculated that a typical smoker inhales 2 mg benzene daily, compared to 0.2 mg/day for the nonsmoker. Thus, cigarette smoking may be the most important source of exposure to benzene for about 50 million citizens of the United States. Passive smokers exposed at work had significantly elevated levels of aromatics in their breath. Indoor air levels in homes with smokers were significantly greater than in nonsmoking homes during fall and winter but not during spring and summer. The average annual increase in homes with smokers was 3.6 microgram/m3 for benzene and 0.5 microgram/m3 for styrene--an approximate 50% relative increase in each case. Thus, exposure to benzene and styrene may be increased for the approximately 60% of children and other nonsmokers living in homes with smokers.