The invention relates to a method for recognizing the respiratory phases of a patient for controlling a ventilating apparatus. The time-dependent trace of a signal, which represents the respiratory flow curve and is emitted by a signal device, is determined and from this trace, a trigger criterium is obtained for the switchover of the ventilating apparatus from the expiration phase into the inspiration phase and/or from the inspiration phase into the expiration phase. The method is improved in that even for chronically obstructive patients, a reliable and early recognition of the inspiration and expiration attempts is possible. A significant increase of the slope of the respiratory flow curve between each two zero crossovers of this curve is used as a trigger criterium.