In a subway system, when a train leaves one station to go to another power consumption increases and, at one point, reaches a peak. When such peaks occur simultaneously, the total power peak of the system can be very large. On the other hand, if departures are totally desynchronized, it could affect the overall operation of the system. This paper deals with the problem of finding a procedure to desynchronize train departures during a typical rush hour operation so that overall power peaks are minimized and the frequency, safety and operational constraints of the system are respected. A formulation of the problem and a heuristic approach are proposed. Results, using operational data from the Montreal subway system, are presented.