Abstract: A method for the manufacture of a light wave guide providing a cladding and a light conducting core, from a glass tube, showing a material on or below its inner surface which forms the core of the finished light wave guide comprising at least one substance which is diffused out selectively of this material, forming the core subsequently, into the interior space of the glass tube, whereby during the diffusing-out process the partial pressure of the diffusing-out substance in the interior space of the glass tube is maintained as small as possible, whereby a premature collapsing of the glass tube during the diffusion process is prevented by adjusting an overpressure in the glass tube, that the glass tube after the diffusing out process is largely collapsed by rinsing with a rinsing gas and in a last collapsing step is completely collapsed to a rod (perform) without rinsing with a rinsing gas and that the rod is subsequently drawn out to a fiber.