A computer-controlled high resolution infrared tunable diode laser (TDL) system has been developed to determine simultaneously the concentration of a smoke component and the filter ventilation of a cigarette during smoking. 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 and to mix this gas with the smoke under actual smoking condition. This is the first study of which we are aware, where the concentration of a smoke component is obtained simultaneously with the dynamic ventilation level within seconds after each puff is taken. Experiments were conducted using cigarettes having different filter ventilation levels. Each cigarette was measured for the static ventilation prior to smoking using the standard pressure drop method. The results demonstrated that 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.