Wang L, et al. - Since biomarkers of tobacco exposure have a central role in studies of tobacco use and nicotine intake, researchers assessed the performance of laboratories conducting measurements of biomarkers of tobacco exposure (mainly nicotine and its metabolites in urine). Eleven laboratories from six countries were involved. Blind replicates of seven human urine pools were assayed in each laboratory, at various concentrations on three separate days. Five pools blended from smoker and nonsmoker urine sources, and two additional blank urine samples fortified with pure nicotine, cotinine, and hydroxycotinine standards, were included as samples. According to the findings, reliable and comparable human urinary nicotine metabolic profiles in samples from people with significant recent exposure to nicotine can be produced by the experienced laboratories participating in this study.