Based on previous work, a method is presented to predict the signature of a CO2laser, i.e., the output power as a function of the cavity length. For that purpose the normalized laser intensity curve versus cavity length is determined for a single line. The calculation is based on a homogeneously broadened line (Lorentzian shape) and takes into account the line dispersion. The curve is a parabola and its shape is assumed as being the same for all lines considered. From calculated positions of line centers and small-signal-gain data the signature can be drawn with the help of a parabolic French curve. The transition from one line to the next is assumed to occur at crossings of the normalized intensity curves. The theory agrees well with the experiment.