Studies in our laboratory revealed artifactual formation of N-nitrosamines during trapping of mainstream and sidestream tobacco smoke by the method of Hoffmann and coworkers (2, 4). Both volatile and tobacco-specific N-nitrosamines were produced. This artifact formation took place on the Cambridge filter, which is part of the collection train used in the previously published procedure. When the filter was treated with ascorbic acid before smoke collection, artifact formation was inhibited. The improved method resulting from these studies was applied to a comparative analysis of N-nitrosamines in smoke from cigarettes that heat, but do not burn, tobacco (the test cigarette) and several reference cigarettes. Concentrations of volatile and tobacco-specific N-nitrosamines in both mainstream and sidestream smoke from the test cigarette were substantially lower than in the reference cigarettes.