For the most common geodetic tasks such as surveying, staking out and monitoring, GNSS RTK method has in many cases been limited by its measuring quality. Combining laser system with GNSS RTK system enables the increase of vertical accuracy of measurement to a millimetre level. Testing the above mentioned systems for height determination will be presented in this paper. Since December 2008 CROatian POsitioning System (CROPOS) has been operational. GPS RTK system combined with laser system has been tested with CROPOS service, because more and more users are using this system in every day geodetic tasks. Testing the vertical accuracy of measuring modes has been done on the calibration baseline of the Faculty of Geodesy in Zagreb. Heights were determined by four different measuring modes; GPS RTK method in combination with laser system, GPS RTK method in combination with laser system linked with CROPOS service (VPPS - Very Precise Positioning Service), GPS RTK method and GPS RTK method linked with CROPOS service (VPPS). The authors of the paper will try to examine whether it is possible to achieve higher accuracy of vertical component when GPS RTK system is combined with laser system. Finally, the advantages, possible disadvantages, and vertical quality comparison of all measuring modes will be shown in this paper