Abstract: In accordance with the invention, the incoming receiver signal is subject to an envelope demodulation by means of a measuring receiver 2. Subsequently, for a defined measurement time T.sub.ges) in defined time differences .DELTA.T, the signal is sampled and digitized via an analog/digital converter 3 and stored in a computer 4 as a consecutive sequence of 1-N values of the square of the envelope function R.sup.2 (t). From these stored values the auxiliary values X' and Y' are generated, whereby Y' is corrected by means of an appropriate correction factor k. Then, the C/I ratio is determined via the proper procedures. The method of the invention distinguishes itself in that, with relatively little expenditure and taking into consideration the typical features of the GSM mobile communication network, and based on the receiving power as a function of time, the C/I ratio is determined from the values of the function of this time function by means of an analytical calculation.