The mass spectra of the tobacco alkaloid-derived nitrosamines NNN, NNK, NNA, NAB and NAtB, and of known mammalian metabolites of NNN, and NNK are presented. Mass spectra of synthetic derivatives related to these nitrosamines and their metabolites are also included. These spectra will be useful in studies on the occurrence and metabolism of the tobacco alkaloid-derived nitrosamines and in investigations of other compounds related to the tobacco alkaloids. (Mass spectrometry )