The invention relates to a method of further developing the measuring of so-called neuromuscular transmission (or NMT), said measuring being effected by stimulating with electric pulses a given muscular nerve, e.g. the ulnar nerve in the arm of a patient, and by measuring a corresponding muscular block by means of EMG. In the prior art NMT-measurings, a stimulus artefact, caused by stimulation and induced directly electrically and independently of a stimulus passing through said muscular nerve, may often distort measuring results. According to the invention, this artefact is not tried to be eliminated by various gate solutions but, instead, it is measured by first effecting a measurement prior to the actual neuromuscular block measurements e.g. in connection with the calibration of the control or reference value of a muscular block and by recording or storing this first value of a stimulus artefact. This is followed by monitoring the changes of stimulus artefact values by measuring said stimulus artefact during the measurements of a neuromuscular junction and by comparing the thus obtained stimulus artefact values with said first value, not only for securing the reliability of measuring information but also preferably for controlling the state variations and condition of NMT-measuring instruments. By digitizing the collected information, the measuring errors can be preferably eliminated mathematically by utilizing data processing.