signiﬁcant reductions in all these products. In fact, these studies have also shown that there is a tight correlation between reductions in exhaled CO and smoke-related particulate matter, suggesting that the use of exhaled CO is, indeed, a good surro- gate in studies with a large number of places and individuals studied. Goodman et al20 showed the effects of the Irish smoking ban on respiratory health of bar workers and in the air quality in Dublin pubs, studying particulate matter in 42 pubs and exhaled CO and salivary cotinine of 81 barmen, before and after the ban law. They showed a signiﬁcant reduction of 83% in particulate matter concentration, a reduction of 79% and 81% in the exhaled CO concentration and in salivary cotinine of non- smokers and ex-smokers, respectively. No changes were seen in current smokers, but there were clear sample size limitations for this analysis. Speciﬁcally, this study showed that after the ordinance, there was a reduction of 70% in the CO concentration in hospitality venues. The reduction was close to threefold in enclosed areas. By comparing the values of CO concentration in the streets monitored by CETESB during the same period of the study, it is possible to understand that the CO concentration reduction observed in such places cannot be attributed to external factors like climatic changes or season variability. The average CO CETESB streets concentration before and after the smoking-ban law was lower than 1 ppm in the study periods. In fact, it is interesting to observe that in the post-ban period CO concen- tration in closed, semi-open and open venue areas became similar to the measured in streets monitored by CETESB. Other important observation of this study was that the exhaled CO for the non-smoking workers became similar to the levels observed in regular non-smoking citizens who live in São Paulo city according to Issa et al,21 but the most relevant observation was that even among smokers who increase ciga- rette consumption after the ban law we found signiﬁcant reductions in the CO concentration of exhaled air, proving that the SHS inﬂuence on the CO concentration in smokers was independent of changes in cigarette consumption. There are some potential limitations. Owing to our sample size we were not able to conduct measures of other biological markers of SHS, such as particulate matter concentrations. In addition, interesting data regarding behavioural changes that led to smoking habit changes in smoking employees were not obtained and we could only measure the result of these changes in the number of cigarettes smoked. Finally, we have little health What is already known on this subject Cardiovascular events are reduced a few months after smoking- ban laws are implemented. Although carbon monoxide (CO) is one of the most important components present in SHS, few studies to date have aimed at quantifying the reduction of CO exposure after smoking-ban laws. What this paper adds We were able to describe signiﬁcant environment and individual reductions in CO concentrations. The effect of the smoke-ban law was detectable in all environments of visited venues and, most importantly, in both non-smoking and smoking employees. Research paper information on studied individuals, which precluded the use of more complex regression models adjusting for potential confounders of the observed changes (eg, prevalent pulmonary conditions, smoking history, etc). The consequences of the observed CO reduction are not well known, but it clearly indicates the unequivocal inﬂuence of SHS in CO exhaled air concentration in individuals who work in these venues. Thus, one can speculate that the signiﬁcant reduction obtained in CO concentrations after adoption of tobacco smoke-free legislation could be causally related to the reduction in cardiovascular events incidence observed in many places where this law has already been adopted. In conclusion, our ﬁndings are consistent both at the envi- ronment and individual levels and they reinforce the necessity for supporting the campaign for tobacco free environments. Acknowledgements S˜ao Paulo State Center of Surveillance agents for the data collected, and Patricia Shigeeda Bossoni for the English support. Funding This study was funded by Funda¸c˜ao Zerbini and S˜ao Paulo State Department of Health. Competing interests JI has consulted for Pﬁzer and has been principal investigator for clinical trials of smoking cessation medications funded by Pﬁzer and other clinical trials funded by Lilly. The other authors report no conﬂicts. Patient consent Obtained. Ethics approval This study was conducted with the approval of the CAPPESQ ethics committee for research project evaluation of the Hospital das Clinicas, School of Medicine, University of S˜ao Paulo. Provenance and peer review Not commissioned; externally peer reviewed. REFERENCES 1. World Health Organization. Conference of the Parties to the WHO Framework Convention on Tobacco Control. http://www.who.int/gb/fctc/PDF/cop2/ FCTC_COP2_17P-en.pdf (accessed 9 Dec 2009). 2. World Health Organization/International Agency for Research on Cancer IARC. Tobacco smoke and involuntary smoking: summary of data reported and evaluation. Geneva. 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