Chronic smokers (of between 4 and 20 years duration) and non-smokers will be recruited. Smokers will be allocated to a "light" group, smoking 4-10 cigarettes per day and a "heavy" smoking group who smoke 11-20 cigarettes per day. Non-smokers will be defined as those with a life time consumption of no more than 20 cigarettes, do not live or work in a smoky atmosphere. All individuals will have a normal history and clinical examination, including a normal EKG, urinalysis and serum chemistry, haemogram and negative urinary pregnancy test.