Project Summary African Americans are more likely than Whites to die from smoking related diseases and are less successful at smoking cessation with the current FDA-approved aids. Thus, this proposal seeks to investigate the use of e- cigarettes on smoking reduction in African American and White smokers. This proposal will elucidate the relationship between nicotine metabolism and nicotine concentrations in e-cigarettes on smoking behavior and toxicant exposure in African American and White smokers. We hypothesize that slow nicotine metabolizers will have higher nicotine plasma levels than normal nicotine metabolizers at all nicotine concentrations and report greater positive subjective effects. Additionally, we hypothesize that slow nicotine metabolizers will be more likely to reduce their smoking with e-cigarettes because studies show slower nicotine metabolizing smokers are more successful on nicotine replacement therapies than normal or fast nicotine metabolizing smokers. The outcomes of the project will provide new information to further develop the knowledge base in understanding which nicotine concentration manufacturers should include in e-liquids to reduce smoking behaviors. Regulatory efforts could cap the nicotine content in e-liquids to reduce the addictive potential of e-cigs to adolescents but provide a harm reduction avenue for smokers, especially African American smokers, to protect overall public health.