EDITOR—In the late 1970s Hoffmann's group described the carcinogenic properties of the tobacco-specific nitrosamines including 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone and N'-nitrosonornicotine in a series of experiments.1 These substances are formed during the curing process by a chemical reaction between nicotine and nitrate. They are present in cigarettes, chewing tobacco, and snuff. One of the substances, 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone, is of particular interest as it is a powerful lung adenocarcinogen in animals regardless of route of administration. Adducts of N'-nitrosonornicotine and 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone are seen in …