Known locks for a secondary leaf of fire doors comprise a pair of rods which slide vertically, in opposite directions, between an extracted closing position and a retracted opening position, and which at their ends engage corresponding seats provided respectively in a door frame and in a floor, a first upper and a second lower slide which can be connected to the rods and guided in a sliding manner vertically in a casing of the lock against respective return spring means between a position of reciprocal withdrawal and a position of approach, corresponding respectively to the closing and the opening positions of the rods, a rocker return device pivoted centrally on a first pivot in the casing and having at opposite ends pin articulation grooves into which project pins from the slides, for transmission of movement from the first slide to the second slide, a second pivot on the casing on which an activating lever pivots to act on the first slide against second return spring means, such as to give rise to movement of the slides into the position of reciprocal approach. In the present invention the activating lever is located within the casing and the front face of the casing is provided with an aperture for extraction of the activating lever.