Abstract: A plate bundle for a heat exchanger, of the type comprising a stack of mutually parallel metal heat-exchange plates (10), each including smooth-surfaced edges and a corrugated central part (11) to form, with the associated heat-exchange plates (10), a double circuit for circulation of two independent fluids in counterflow. The plates (10) are connected to one another at their longitudinal edges by connection means (13) and comprise, a zone of heat transfer and exchange between the fluids and, at their free ends, a zone for inlet and outlet of the fluids. The fluid inlet and outlet zones are formed by the plane ends (10a) of the heat-exchange plates (10), between which independent plates (21) provided with reliefs for distributing the fluids in the heat-exchange zone are inserted.