Int. J. Environ. Res. Public Health 2009, 6 1634 effects on cancer, cardiovascular disease and respiratory disease [1,2]. More specifically, SHS exposure has been shown to cause lung cancer [3], respiratory disease, particularly in children [4,5], and heart disease [6-8]. Recent evidence adds breast cancer in young women to the list of SHS related diseases [2]. Three recent studies have used the National Health and Nutrition Examination Survey (NHANES) data to estimate SHS exposure in the U.S. Pirkle and his colleagues [9] analyzed the NHANES III data from 1988-1991 and showed that serum cotinine levels indicate broader exposure to SHS than self- reported data. They found that the highest cotinine levels were for children, non-Hispanic Blacks, and adult males. In a later study, Pirkle and colleagues looked at trends in SHS exposure from 1988-2002 using serum cotinine concentration, and found that there have been substantial declines in exposure over this time period, though children and non-Hispanic Blacks have higher levels of exposure than others [10]. Schober, Zhang, and Brody [11] compared SHS exposure between 1988-94 and 1999- 2004. They found that the percentage of nonsmokers with self-reported home exposure and the percentage with detectable serum cotinine declined between the two time periods. The rate of decline was smallest for children followed by adolescents. An analysis of the National Health Interview Survey found that SHS exposure at home, measured as the number of days per week someone smoked in the home, declined more substantially between 1992 and 2000 than would be predicted by the decline in active smoking [12]. Using data from the Medical Expenditures Panel Survey (MEPS), Machlin, Hill, and Liang [13] report that children who were older, poorer, and lived with adults with less education, were most likely to be exposed to SHS at home, as indicated by their living with at least one adult smoker. They do not report whether or not the person actually smoked inside the home. Studies that compare the rates of exposure to SHS among racial/ethnic groups have generally found that among nonsmokers, African Americans have the highest rates of exposure. This has been reported for young adults using both cotinine concentration and self-reported number of hours of exposed per week [14], for women using self-reported number of days exposed per week [15], and for children using urinary cotinine levels and self-reported number of hours exposed [16]. However, it must be noted that when socioeconomic indicators were taken into consideration in one study, the higher rate of exposure among African American women was no longer found [15]. Hispanics have been found to have relatively low exposure rates, using both cotinine concentration and self-reported number of hours exposed [16]. Among nonsmoking Hispanic women of reproductive age, exposure to SHS differed by country of origin, according to an analysis of the Hispanic Health and Nutrition Examination Survey [17]. Exposure at home, indicated by whether or not someone in the household smoked, was found to be 31-62% for Mexican-American women, 22-59% for Puerto Ricans, and 40-53% for Cuban-Americans during 1982-1984 in the U.S., depending on age. For all groups, the youngest women (age 12-19) had the greatest exposure. For Mexican-Americans, exposure decreased with age, but for Puerto Ricans and Cuban-Americans, the pattern was less clear. At work, exposure was indicated by whether or not the respondent worked near someone who smoked in their presence. Work exposure was 22-35% for Mexican-Americans, 28-33% for Puerto Ricans, and 33-49% for Cuban Americans during the same period from 1982-1984. There was no pattern for work exposure by age. Pirkle and colleagues [9] reported that non-Hispanic Blacks had the highest exposure to SHS according to both serum cotinine measures and self-reported exposure. Findings from an analysis of