Research paper the pre-ban survey, and many surveyed individuals in the pre-ban survey were off-duty on those days or some of them were no longer employed at the venue. It should be mentioned that no signiﬁcant difference in mean CO levels between indi- viduals who were revisited or not revisited was observed (p¼0.23, CO mean level of 10.47 and 11.44 for revisited and not revisited individuals, respectively). As expected, a signiﬁcantly higher mean CO level was observed in employees who smoked than in employees who did not smoke (p<0.001 in the pre-ban survey; p<0.001 in the post- ban survey). In the pre-ban period, signiﬁcant correlations were observed between measured CO level in indoor environments and expired CO levels in both smoking (p<0.001) and non- smoking employees (p<0.001). It is interesting to note, however, Figure 2 Relation between exhaled CO levels in smoking and non-smoking venue employees (X axis) and environment CO levels of visited venues (Y axis). (A) Non-smoking employees pre-ban period; (B) Smoking employees pre-ban period; (C) Non-smoking employees post-ban period; (D) Smoking employees post-ban period. Tobacco Control 2011;20:156e162. doi:10.1136/tc.2010.037614 159