This International Standard is applicable to the determination of carbon monoxide present in the sidestream smoke from cigarettes. The described method is specified using the ISO 3308 smoking parameters (puff volume, duration and frequency) and butt length, but it is technically compatible with other smoking regimes. NOTE The method may not be directly adaptable to other sidestream smoke analytes. Nevertheless the determination of carbon dioxide was part of the validation study of ISO 20774 carried out by CORESTA. According to the number of reporting laboratories no rigorous statistical analysis of sidestream carbon dioxide data was carried out. Therefore only indicative information about conditions for the determination of CO2 is provided.