The authors describe a new automatic gain control (AGC) system for MFSK modems. The AGC system is a multi-tasking system in which the control gain is derived directly from the detection stage of the MFSK demodulator. The AGC system also evaluates the channel signal to noiseratio (SNR) and the level of inband interference. The theoretical and simulation studies of the behaviour of the system under additive white Gaussian noise (AWGN) channel conditions is presented