Machine parts are laser treated by cladding, alloying or hardening, depending on the wear conditions. During these thermal laser treatments, gases and particles are emitted from the workpiece and the supplementary materials used. These emissions have been investigated. Typical filler powders contain high amounts of Co, Ni, Fe, lu and A] for cladding, and W, Mo, V and Co for alloying. The results show that the chemical composition of the emitted aerosol is similar to that of the filler materials, with a few exceptions. The amount of fume fraction of aerosol emission per deposited filler material increases with the supplied energy, while the dust fraction remains constant. Mixtures of anorganic and organic components are the usual absorbent coatings for the hardening. The anorganic components are oxidized and/or partly evaporated and condensed, the organic components are pyrolyzed or partly burned. The aerosol emission rate increases with the coverage rate for a given surface temperature . The main emission components are benzene, phthalic acid anhydride as well as organic and anorganic fumes. The particle size distribution has nearly the same characteristics for the three laser surface treatments and all investigated materials. The relative mass frequency has a maximum at an aerodynamic diameter range 0.06 - 0.5 gm. A large fraction of the aerosols is respirable. Without exhaustion the threshold limit values can be reached or exceeded for the emitted fumes as well as for special elements and compounds such as cobalt, copper, nickel and benzene. The installation of suitable exhaustion systems is inevitable.