A differential equation has been developed representing the different processes contributing to the steady state thermal equilibrium in a smouldering cigarette. As conceived, the expression consists of a heat production term, a radiative heat loss term and four terms representing the various endothermic processes that take place in the cigarette cone. The heat production rate of an average tobacco column was estimated to be about 120 cal per min. and the radiative heat loss about 90 cal per min. with the balance being used in the various endothermic processes that are involved in advancing of the burning cone.