The nicotine concentration in samples of house dust from the homes of 34 smokers and 38 nonsmokers was analyzed using a gas chromatographic method. A strong positive correlation (r = .65, p less than .0001) between the amount smoked and the nicotine concentration in the house dust was found when the results from all homes were analyzed, and a fairly strong positive correlation (r = .35, p less than .05) was found for smokers' homes only. These data suggest that the nonsmoker may inhale tobacco constituents from respirable dust, even if smoking does not occur. The amount of nicotine inhaled during 1 h was estimated for someone in one of the homes where there was a high nicotine concentration in the house dust. The calculated amount, 12 ng, is very small compared with the amount inhaled when active smoking occurs (i.e., 600-3,000 ng/h). In this study, nicotine was a marker of tobacco pollution. Assuming that other tobacco smoke agents have a similar or smaller affinity to house dust as that of nicotine, we conclude that house dust inhalation constitutes only a modest additional source of involuntary smoking.