Cigarette smoking is a major contributor to morbidity and mortality. Although intensive efforts have been made to develop effective smoking cessation techniques, many people have been unwilling or unable to maintain nonsmoking. Efforts to impove the success of cessation programs have been hampered by the lack of a suitable objective measure of smoking status, and much recent interest has been directed toward this issue. Of the indices developed, thiocyanate (SCN) has become the most widely used. SCN results from the metabolism of cyanide, a major ciliatoxic agent in cigarette smoke. SCN may not only reflect an individual's exposure, but also an individual's ability to detoxify a constituent of tobacco smoke that is associated with lung disease. The overall purpose of the proposed research is to determine the influence of selected variables on salivary SCN in order to improve its accuracy as an indicator of smoking status, and to explore factors involved in metabolism of hydrogen cyanide. Three studies are planned. The first will provide a more detailed examination of methodological issues than has been done to date, and should help to improve the reliability of the measure. The second study is designed to determine whether smoking of marijuana can yield false positives and, if so, the time course of the effect. The final study is designed to examine, in depth, the pattern of changes in SCN during the process of smoking cessation. Measures of SCN, nicotine, cotinine, smoking behavior, nonsmoking exposure to cyanide, and dietary sources of SCN will be obtained from 80 individuals before cessation and for 3 months after cessation. Both successful and unsuccessful subjects will be followed for the entire period. The findings of this research may yield both a more valid index to evaluate smoking cessation programs and information on individual differences in the way smokers metabolize one of the agents associated with lung disease. This document is a resubmission of a proposal previously reviewed by the Behavioral Medicine Study Section. Discussion of issues raised in the original critique is included in the introduction to the Research Plan.