Some methods of virus purification are discussed. A distinction has been made between the purification, which can be obtained in a rather simple way (e.g. of the viruses of tobacco mosaic, tomato bushy stunt and turnip yellow mosaic) and that, which require a more complicated manipulation (e.g. of the potato virus X). Information is given about the concentration through salting out with ammonium sulphate of the virus causing the „ratelziekte” of tobacco. Previously the normal cell constituents had been mostly removed by heating the expressed sap of diseased tobaccoplants during 10 minutes at 60°C and then centrifuging off the coagulum. The partly purified virus (a brown, amorphous product has been obtained) could be preserved at 12°C during at least 3 months without losing infective power.