In the past the brightest prints on viscose rayon have been obtained with acid and direct dyes, but these lack washing fastness, and many of the brightest acid dyes are also fugitive to light. The author shows how basic dyes, hitherto notoriously fugitive to light, may be printed by a new all-in method, resulting in the deposition within the fibres of colour lakes of molybdophosphoric acid. A number of stages in the development of this new printing technique are described, and are related to the earlier development of the manufacture of similar lakes in pigment form. The new prints are fast to light and washing, and may be supplemented where necessary by use of insoluble azo dyes applied by suitable methods. LAT=English