We have developed a new theory of how nicotine from cigarette smoke evaporates and subsequently deposits in a denuder tube, and we have applied that theory to the analysis of denuder tube experiments. We find that for the special case where gas-particle equilibrium exists in all parts of the denuder and follows Henry's Law, the differential equation governing deposition in the denuder is readily solved analytically. A criterion for ensuring the validity of the equilibrium assumption was derived, and found to be satisfied by nicotine in cigarette smoke. Application of the theory to experimental data shows that the theory predicts the deposition pattern in a denuder, that most deposition of nicotine from smoke is due to evaporation, and that the percentage of nicotine initially in the gas phase is about 0.1%, less than previous estimates by an order of magnitude. (C) 2003 Elsevier Ltd. All rights reserved.