The behaviour of active carbon beds has been investigated under dynamic conditions, for the removal of organic vapours from dry air at 293 K and 3-7 atm. A simple relation is found for the rate constant of desorption at 1 atm, taking into account the properties of the vapours and the active carbons. Previsions can therefore be made for the behaviour of the system under PSA conditions, on the basis of an analytical model and a numerical model. A good agreement is found with the experimental results.