Abstract: A heat exchanger using a stack of plates with sealed flow spaces between them utilizes a multiplicity of plates that fit flush together at their perimeters and are provided with profiling by stamping. They are essentially the same in shape and are alternately rotated, in the planes of the respective plates, by 180.degree. with respect to each other for stacking. Before they are compressed into a stack, sealing profile members are inserted which fit into grooves for providing a perimeter seal. The flow spaces between the plates serve alternately for a first and a second fluid medium, which are guided in parallel counter-current through the stack, passing through perforations in the corners of the plates. At least part of the plates are thus releasably stacked with removable sealing profile members. The removable perimeter seals between plates are constituted as multiple seals having at least two profile members at a substantially constant distance from each other.