An estimated 434,000 deaths per year in the U.S., or more than one of every six deaths, are attributable to tobacco use, in particular cigarette smoking (CDC, 1991a; figures for 1988). Approximately 112,000 of these smoking-related deaths are from lung cancer, accounting for an estimated 87% of U.S. lung cancer mortality. Cigarette smoking is also causally related to cancer at various other sites, such as the bladder, renal pelvis, pancreas, and upper respiratory and digestive tracts. Roughly 30,000 deaths per year from cancers at these sites are attributable to smoking. Furthermore, smoking is the major cause of chronic obstructive pulmonary disease (COPD), which includes emphysema, and is thought to be responsible for approximately 61,000 COPD deaths yearly, or about 82% of COPD deaths. Tobacco use is also a major risk factor for cardiovascular diseases, the leading cause of death in the U.S. It is estimated that each year 156,000 heart disease deaths and 26,000 deaths from stroke are attributable to smoking. In addition to this substantial mortality, the association of smoking with these conditions also involves significant morbidity. Smoking also is a risk factor for various respiratory infections, such as influenza, bronchitis, and pneumonia. An estimated 20,000 influenza and pneumonia deaths per year are attributable to smoking. Smokers also suffer from lung function impairment and numerous other respiratory symptoms, such as cough, phlegm production, wheezing, and shortness of breath. In addition, smokers are at increased risk for a variety of other conditions, including pregnancy complications and ulcers. Although the exact mechanisms and tobacco smoke components associated with these health effects are not known with certainty, more than 40 known or suspected human carcinogens have been identified in tobacco smoke. Many other toxic agents, such as carbon monoxide, nitrogen oxides, ammonia, and hydrogen cyanide, are also found in tobacco smoke. Smokers, howe