A challenging task in using pedestrian navigation and guidance services indoors is to determine the correct floor of a user in a multi-storey building because most indoor location techniques only provide 2-D information. In this case it can be recommended to augment the position determination system with a barometric pressure sensor for direct observation of height differences. In the research project NAVIO (Pedestrian Navigation Systems in Combined Indoor/Outdoor Environments) tests with different sensors have been performed and their results are presented. The tests show that it is possible to determine the correct floor of a user using a barometric pressure sensor as the standard deviation of the estimation of the height differences is better than ± 1 m.