U.S. Patent 4,888,977. Assigned to Koerber AG, Hamburg, Germany. The degree of ventilation of ventilation zones in the wrappers of filter cigarettes is ascertained by confining the ventilation zones of successive cigarettes in a chamber during travel through a testing station and by increasing the pressure in the chamber above or by reducting the pressure in the chamber below atmospheric pressure. The pressure at that end of each cigarette which is adjacent to the ventilation zone is monitored at the testing station, and the resulting signal is indicative of the degree of ventilation. Such signal can be divided by a signal denoting the pressure in the chamber during testing, and the resulting signal can be multiplied by 100 to obtain a signal which is indicative of the degree of ventilation in percent. The signal which denotes the degree of ventilation can be displayed, used to modify the operation of the apparatus which provides the wrappers of cigarettes with ventilation zones, and/or used to segregate cigarettes with unacceptable ventilation zones.