Abstract: A rotary evaporator for evaporating a substance contained in an initial substance comprises an evaporation flask (2) for receiving the initial substance, a device (3) for heating the substance, a condenser (4) for condensing the vaporized substance, a collection container (6) for receiving the re-liquefied substance and at least one device (5) for generating a low pressure and/or an excess pressure. In order to remove the re-liquefied substance an excess pressure can be generated at least within the collection container (6) and/or in order to remove residues of the initial substance an excess pressure can be generated at least within the evaporation flask (2).