Diffusion of cadmium, magnesium and sulfur in ZnSe-based quantum well structures is studied by thermal treatment under different ambient atmospheres and depth selective ion implantation. Secondary ion mass spectroscopy analysis and X-ray diffraction demonstrate that metal components diffuse via group II lattice sites already at temperatures below 500 degrees C. Both. p-type doping and the generation of group II vacancies induce a strong enhancement of diffusion. The more stable group VI element sulfur diffuses by a kick-out mechanism. Diffusion coefficients for different annealing and doping conditions are determined and the consequences for device design are discussed.