Agricultural machinery drivers are exposed to low-frequency vibrations during their work. The terrain profile, the long operating times, the forward speed of the agricultural machine and the sitting position are the key factors that lead to the suffering of the back of the agricultural machinery drivers. Suspensions systems are produced in order to reduce the health risks and the discomfort to the driver and to enable the driver to work at a faster pace. The suspension systems isolate the driver from the machine vibrations as much as possible. Modelling the motions of the suspension systems is useful to acquire insight in the dynamic characteristics of these suspensions and for design purposes. In this paper, a linear model of a cab suspension of a self-propelled agricultural machine with six degrees of freedom is developed, based on Lagrange's equation. The model takes into account the kinetic energy of the suspension and the virtual work executed on the cab suspension. The model of the cab suspension is validated by comparing the behaviour of the model with the behaviour of an experimental test rig for different vibration signals. (C) 2004 Silsoe Research Institute. All rights reserved Published by Elsevier Ltd.