Tobacco-specific nitrosamines (TSNAs) are one of the major classes of carcinogens found in tobacco products. As part of collaborative efforts to reduce tobacco use and resulting disease, the U.S. Centers for Disease Control and Prevention (CDC) carried out a two-phase investigation into the worldwide variation of the levels of TSNAs in cigarette tobacco. In the first phase, representatives of the World Health Organization (WHO) purchased cigarettes; scientists from the CDC subsequently measured the levels of TSNAs in tobacco from 21 different countries. Although the data collected from this initial survey suggested that globally marketed U.S.-brand cigarettes typically had higher TSNA levels than locally popular non-U.S. cigarettes in many countries, the number of samples limited the statistical power of the study. To improve statistical power and to ensure adequate sampling, the CDC conducted a second survey of 14 countries. In addition to the United States, the CDC selected the world's 10 most populous countries and three additional countries, so that at least two countries from each of the six WHO regions were represented. For each country, the CDC compared 15 packs of Marlboro cigarettes, which is the world's most popular brand of cigarettes, with 15 packs of a locally popular non-U.S. brand in the study country. Marlboro cigarettes purchased in 11/13 foreign countries had significantly higher tobacco TSNA levels than the locally popular non-U.S. brands purchased in the same country. The findings suggest that TSNA levels in tobacco can be substantially reduced in some cigarettes.