Twenty-five brands of Canadian commercial cigarettes were analyzed for tobacco-specific nitrosamines (TSNA) in tobacco and in mainstream smoke as well as for nitrate in tobacco. Preformed N'-nitrosonor-nicotine (NNN) in the tobacco ranged from 265 ng to 979 ng/cigarette, preformed 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) ranged from 465 ng to 878 ng/cigarette. The mainstream smoke concentration for NNN was between 5 ng and 39 ng/cigarette and for NNK between 5 ng and 97 Ng/cigarette. The nitrate levels were between 0.3 mg and 3.4 mg/cigarette. The NNK levels in tobacco and in mainstream smoke were higher than the NNN levels, which is typical for Virginia-type cigarettes. Based upon the average mainstream smoke concentration of the three most popular Canadian cigarette brands, an average TSNA delivery for 20 cigarettes of 0.7 micrograms NNN and 1.7 micrograms NNK can be calculated, which is less than the average for West German cigarettes. The results of this investigation demonstrate that there seems to be a good correlation between the TSNA and tar deliveries in mainstream smoke. However, no correlation between the level of preformed TSNA in tobacco and the tar delivery in mainstream smoke could be observed. It is demonstrated that the good correlation between the tar and TSNA deliveries in mainstream smoke can only be attributed to the unusual good correlation between the tar delivery and the ventilation ratio. For the cigarettes investigated, which seemed to be Virginia-type cigarettes, with few exceptions, the ventilation ratio had a much higher influence on the mainstream smoke concentration than the level of preformed TSNA in tobacco.