Many smoke constituents are generated from the pyrolysis of tobacco leaf components. To understand the formation mechanism of smoke constituents, it is important to reveal which tobacco component provides the biggest contribution to the generation of each smoke constituent. In the present study, the precursors of smoke constituents were examined using the tobacco pyrolysis model. The amounts of main tobacco components in flue-cured and burley tobacco were analyzed (sugars, protein, polyphenols, alkaloids, organic acids, inorganics etc), and each of the components was added to the tobacco at the 0.5-fold and 1.0-fold amount of the tobacco leaves. The treated tobacco samples were then pyrolyzed up to 800 degrees centigrade in nitrogen with an infrared image furnace, and the generated smoke constituents (benzo[a]pyrene, hydrogen cyanide, carbonyl compounds, aromatic amines, volatile organic compounds and phenolics) were quantitatively determined with GC-MS, HPLC etc. The contribution of each tobacco component to the generation of smoke constituents was investigated as follows. For example, the amount of chlorogenic acid (CGA) in the flue-cured tobacco was 7.6 mg per g-tobacco. When 3.8 mg of CGA (0.5-fold) and 7.6 mg of CGA (1.0-fold) were added to the flue-cured tobacco, the generation of phenol was increased by 14% and 24%, respectively. A regression line was made from the three sets of data (no CGA addition, 0.5-fold CGA addition and 1.0-fold CGA addition), and so the decrease of phenol, when CGA was completely removed, was calculated at 25%, which was defined in our study as the contribution of CGA to the phenol generation in flue-cured tobacco. Since the 0.5-fold and 1.0-fold additions of protein (8.0 mg per g-burley tobacco) showed an increase of 1-aminoanpthalene by 37% and 65% respectively, it was estimated that protein was responsible for 63% of 1-aminonapthalene generation in the burley tobacco. These results provide useful and comprehensive information on the precursors of smoke constituents.