THE various methods and media used for rearing houseflies1 each give results considered satisfactory by the individual workers or laboratory, but no rearing procedure is yet accepted as standard. The Chemical Specialties Manufacturers' Association rearing medium and procedure2 are often accepted in North America but do not appear to be used elsewhere. The rearing procedure evolved in this laboratory3 has since been modified in the various ways described in a–d below, and is now probably simpler and easier than any previously described.