The purpose of this study was to learn how cellulose pyrolysis was affected by changes in atmospheres, by varied pyrolysis temperatures, by the addition of inorganic materials, and by chemical modifications of the cellulose molecule. These studies have led to the hypothesis that cellulose can pyrolyse by two different modes to form B(a)P. Large quantities of B(a)P can be formed by high temperature (850°C) isothermal pyrolysis of cellulose via a very efficient gaseous reaction route. In this reaction the B(a)P yield decreased in the presence of iron, cobalt, and nickel while the yield increased with increasing temperatures and with the introduction of oxygen into the system. In contrast, graduated heating experiments demonstrated that B(a)P began to form at 450°C. This reaction was inefficient with respect to B(a)P yield and was unaffected by the presence of metals. The B(a)P precursors were hypothesized to be nonvolatile, being formed via a solid state decomposition of cellulose and involving the generation of free radicals. This reaction was inhibited by the presence of nitric oxide or salts generating nitric oxide. Additionally, oxidation of the cellulose molecule at the C6 position produced a decreased B(a)P yield.