An isochoric apparatus and a densimeter with a magnetic suspension coupling were used to measure the density of dry air at (10, 30, 75, and 120) kg center dot m(-3). The results are compared with the Zittau database (Kretzschmar, H.-J., et al. Property Data Base for Humid Air, version 2.0; 2004) and the work of Lemmon et al. (Lemmon, E. W., et al. J. Chem. Ref. Data 2000, 29, 331-384) (NIST standard reference database REFPROP 7.0) as well. The humid air was obtained by adding the synthetic air to a gravitationally determined amount of water. It is important to avoid condensation in the part of the apparatus permanently connected to the measuring cell. For that reason, measurements on humid air were carried out using the isochoric apparatus only. Four isochores were measured in the gaseous region at (30, 60, 86, and 107) kg center dot m(-3) with a mole fraction of water in humid air of (4.45, 4.46, 4.20, and 1.26) %. The results are compared with the Zittau database.