During the past decade, larvae of the housefly, Musca domestica L., have been reared routinely in a medium containing two parts of wheat bran and one part of alfalfa meal, moistened with a yeast suspension and a solution of malt euuact. The recent appearance of a standard mixture of wheat bran (33.3 per cent), alfaIfa meal (26.7 per cent), and brewers grain (40.0 per cent), called CSMA (formerly NAIDM), has further simplified the rearing of this species of fly. This note reports a modification of the CSMA medium and its use in the sterile culture of housefly larvae.