Service loading of gears is complicated and contains in general two main modes, namely contact fatigue on gear sides and bending fatigue at teeth toots. One of the promising advanced technology with a potential to increase resistance to both modes of loading is surface laser hardening of gears. The paper deals with an investigation of surface laser hardening characteristics on contact and bending fatigue resistance of a 42CrMo4 steel, being often used for manufacture of gear wheels. The aim of the experimental programme was to simulate the complex service loading of fairly large gears by two separate investigations, namely contact fatigue performed on a special, so called analogon machine and bending fatigue performed on high cycle fatigue resonance machines using three-point-bend (3PB) fairly large specimens. It was shown that after optimising the methodology and parameters of the laser hardening technology, contact fatigue resistance is very good, comparable with very expensive and time consuming thermochemical high-depth surface treatments. Bending endurance limit can be increased. The role of residual stresses resulting from the laser treatment was shown as important, particularly if the steel contains fairly large inclusions – impurities.