Tobacco was extracted sequentially with hexane and methanol-H2O, and the extracts were pyrolyzed at 650 °C in order to identify likely leaf precursors to the tobacco smoke cocarcinogen catechol. The results demonstrated that the methanol-H2O extract and the extracted tobacco residue were good pyrolytic precursors to catechol. Subfractions of the methanol-H2O extract were isolated by HPLC and pyrolyzed. Fructose, glucose, sucrose, and chlorogenic acid were thus identified as important pyrolytic precursors to catechol. Cellulose, a component of the extracted tobacco residue, was also found to be a good precursor to catechol in pyrolysis experiments. To determine the role of these substances as precursors to catechol under the conditions prevailing in a burning cigarette, either [14C(U)]cellulose, [14C(U)] fructose, or various levels of the unlabeled polyphenols chlorogenic acid or rutin were added to cigarettes and the mainstream smoke was analyzed for [14C] catechol and catechol. On the basis of these experiments, we estimated the minimum contributions of these compounds to mainstream smoke catechol levels as follows: cellulose, 7-12%; total of fructose, glucose, and sucrose, 4%; chlorogenic acid, 13%; rutin, 1%. It is suggested that a significant portion of the remaining catechol in mainstream cigarette smoke is formed from pectin, starch, and hemicellulose.