It has been alleged that tobacco companies add ‘ammonia forming compounds’ to cigarette tobacco to "increase as well as control the delivery of the alkaloid nicotine to the respiratory tract of the smoker". It is claimed that such compounds make tobacco smoke more alkaline (higher smoke ‘pH’), thereby increasing volatile nicotine levels. In this presentation the ‘issue’ will be considered, aspects of smoke chemistry will be examined and fundamental problems surrounding the concept - and use of - smoke ‘pH’ will be explored. In particular, experimental results will be described relating to the retention of nicotine and solanesol in the respiratory tract of human smokers according to inhalation depth and duration.