SUMMARYLettuce mosaic virus (LMV) was partially purified from homogenates of infected lettuce leaves in 0·5 M sodium borate buffer (pH 7·5) containing 0·1% thioglycollic acid. The filtered homogenate was clarified by adding butanol and the virus was concentrated and partially purified by differential centrifugation. Such preparations were infective at dilution up to 10‐3. Comparable preparations made in potassium phosphate buffer were not infective.Electron‐micrographs showed the virus preparations to contain long, flexuoiis particles with a mean length of 746 and width of 13 mμ. Antisera made by injecting such preparations intravenously into rabbits precipitated specifically with the preparations and with extracts from infected