A computer-controlled high-resolution infra-red tunable diode laser (TDL) system has been developed to determine simultaneously the concentration of a gaseous smoke component (carbon monoxide) and the filter ventilation of a cigarette during smoking. The simultaneous monitoring of these two parameters provided information which can lead to enhancing the successful development of new cigarette products. The approach selected was to place a cigarette with the ventilation holes of the filter in a chamber filled with a gas not normally detected in cigarette smoke, such as nitrous oxide (N2O), and to mix this gas with the smoke under actual smoking conditions. The N2O provided information concerning the ventilation level and the representative smoke component provided information about the mainstream smoke delivery. This is the first study of which we are aware where the concentration of a smoke component was obtained simultaneously with the dynamic ventilation level within seconds after each puff was taken. Experiments were conducted with cigarettes having different filter ventilation levels (0 %, 13 %, 30 %, 40 %, 60 %, 75 % and 90 %). Each cigarette was measured for the static ventilation prior to smoking using the CORESTA standard ventilation method. These values were in good agreement with those obtained using the TDL. The data collected during this study confirmed that the concentration of the mainstream component investigated increased as the filter ventilation decreased from 90 % to 0 %. With respect to puff number, the ventilation increased slightly during the first puffs then decreased for the later puffs, while the delivery of the smoke component monitored increased with increasing puff number. The 40 % ventilation cigarette showed the largest change in ventilation during smoking compared with the value for the unlit puff.