Nowadays CO2 lasers cover a wide range of power, up to several kW pure light power. Such high power lasers are mostly applied in production to cutting and welding. As the rated output power of industrial lasers has increased considerably within recent years new fields of application, e.g., surface treatment of metallic materials, have become more and more interesting. An essential property of machine tools is their estimated tool life under mechanical stress, which can be increased to a great extent by adequate surface treatment. Such processes are hardening, alloying, or cladding. This paper deals with some aspects of hardening by remelting the surface. During these experiments five different steels were laser treated. In order to achieve high rates of hardness the workpieces were then heat treated additionally. Microstructures and hardness profiles are discussed.