Method for manufacturing a heat exchanger, wherein two neighboring metal tubes (1) are joined to one another in the overlap areas at their open ends by a U-shaped end tube (3), using an adhesive (5), wherein a) the adhesive is applied to the overlap areas of the U-shaped end tube, and wherein the adhesive is selected so that after being applied to the overlap areas of the U-shaped end tube and before being bonded to the metal tubes, the adhesive is solid and not tacky at temperatures below 30° C. and does not cure without an activation step, b) the end tube with the overlap area and the adhesive applied thereto is attached to the metal tubes or inserted into the metal tubes, and c) the adhesive is activated thermally or by bombardment with high-energy radiation either before or after step b), so that it cures after step b) and bonds the metal tube to the U-shaped end tube in the overlap area.