The invention relates to a system for administering muscle relaxant to a patient. The system includes an infusion pump (102) adapted for delivering said muscle relaxant to a patient, and a controller (101) adapted for controlling the operation of said infusion pump on the basis of at least one received input value. Further the system includes measuring means (103) adapted for continuously measuring the effect of said muscle relaxant on the patient, and adapted for supplying a value representing said measured effect as said input value to said controller. According to the invention, on basis of said at least one input value, said controller is adapted for selecting a control value from a set of predetermined control values as the value to be used for controlling said infusion pump. The invention also relates to a method of administering muscle relaxant to a patient, and to a testing apparatus adapted to be used for testing the operation of a system for administering muscle relaxant to a patient.