Abstract: Ion cyclotron resonance is an important method used in mass spectroscopy. Examinations for determining the reactions between substances by means of the two-dimensional ICR method are carried out using the following measuring sequence:P.sub.1 -t.sub.1 -P.sub.2 -T.sub.m -P.sub.3 -t.sub.2,wherein P.sub.1, P.sub.2 and P.sub.3 are rf pulses, with the rf pulses P.sub.1 and P.sub.2 having the same frequency, t.sub.1 and T.sub.m are time intervals between the pulses and t.sub.2 is the observation time following the last pulse. This measuring sequence is repeated several times while varying t.sub.1. In this manner, a plurality of induction signals recorded during the time t.sub.2 is obtained, from which then a two-dimensional spectrum is derived by transformation from the time domain into the frequency domain. The transformation from the time domain to the frequency domain can be effected by two-dimensional Fourier transformation, or with the aid of the method of maximum entropy.