Cigarette emission yields have often been used to compute ETS exposures in indoor environments, but this approach rests on many assumptions and experimental results in this domain vary widely. In order to gain more insight into this field, the following study was performed : The emission yields from the sidestream smoke of experimental cigarettes with different filter ventilations were measured in a first step using a single cigarette collection device. The sidestream smoke from these cigarettes was then released into a room-size, air-tight chamber, and the resulting air concentrations were measured. Eventually, the same process was repeated in a room of an air conditioned office building; in this case both sidestream only and sidestream plus exhaled mainstream (human smoking) were investigated. Different smoke generation rates and various air exchange rates were tested. The results from those sets of experiments are compared and some implications for exposure assessment are discussed.