Abstract: A method for modernizing the control system of a bank of elevators, wherein in a first stage, the elevators are connected to work under elevator-specific computers controlled by a control system comprising a group controller and communicating by means of at least one serial communication bus. The connection is effected using passive adapters between the computers and the old elevator controller. For completing the modernization process of the individual elevators, the elevator-specific functions are modernized by replacing their old functions with functional modules and/or by adding functional modules performing new functions. The functional modules are connected to the elevator computer on a serial bus, one at a time, for gradually replacing the old elevator circuits connectable to a serial communication bus.