The investigatons described in the Report have been carried out at the National Physical Laboratory, Teddington, under the supervision of the Engineering Co-ordinating Research Board of the Department of Scientific and Industrial Research, following an enquiry by a Government Department as to the best material for the preservation of the bright steel parts of stored machinery. A preliminary examination of a number of representative rust preventing mixtures showed that lanoline was superior to the other materials tested. The present investigation on lanoline rust preventers was carried out in order to determine the best solvents for use in lanoline mixtures having regard to initial cost, safety in use and efficiency of the mixture. An examination of samples of lanoline from various sources and tests over long periods under the usual conditions of storage have also been made. The report describes the various tests mand and concludes with details of mixtures which have been found most satisfactory and with specifications for the necessary materials reproduced in part from specifications published by the British Engineering Standards Association by the courtesy of that Association. An abstract of the report of the preliminary investigation and the method of test adopted is given in the introduction to this report.