Abstract The Biomarker Core provides state-of-the-art expertise and technology for the quantitation of metabolites of nicotine and tobacco smoke toxicants and carcinogens. This Core, housed in the new Cancer and Cardiovascular Research Building of the Masonic Cancer Center, University of Minnesota, is equipped with 14 mass spectrometers of various designs and has decades of experience in the application of mass spectrometry techniques for the measurement of metabolites of tobacco smoke compounds and other environmental agents. The following compounds (biomarkers of toxicant exposure and toxicants in the products) will be quantified in this core: 1. Total nicotine equivalents, the sum of total nicotine, total cotinine, total 3′-hydroxycotinine and nicotine N- oxide in urine ("total" refers to the free analyte and its glucuronide conjugate). These compounds account for >85% of the nicotine dose. 2. Total 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), the sum of free NNAL and its O- and N- glucuronides. NNAL is a metabolite of the tobacco-specific lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)- 1-butanone (NNK), found in the urine of all tobacco users, but never in non-users unless they have been exposed to secondhand tobacco smoke. 3. Mercapturic acids of the toxicants acrolein, crotonaldehyde, benzene, and acrylonitrile. 4. Anatabine, a minor tobacco alkaloid to be used to quantify the use of usual brand cigarettes when the study requires the use of very low nicotine content cigarettes (low in anatabine), but allows the use of e-cigarettes or nicotine replacement therapies (NRT). 5. The ratio of 3-hydroxycotinine to cotinine in saliva as a measure of nicotine metabolism, 6. Toxic and carcinogenic constituents in smokeless tobacco and in e cigarette liquid and vapor: nicotine, anatabine and other minor tobacco alkaloids, NNK, and volatile toxicants acrolein, crotonaldehyde, benzene, and acrylonitrile.