Eight yrs.'' experience with the rearing of Lucilia sericata in large numbers in the laboratory has led to the development of convenient apparatus and procedures which are fully descr. Fish heads for the larvae, and water, sugar and fish heads for the adults, are cheap and nutritionally satisfactory foods. The various stages, particularly the prepupal, may be retarded by chilling. The times required after emergence for the first egg deposition were 6 days at 34[degree]C and 21 days at 19[degree]C. The graph of temp.-reciprocal of time for this period was a straight line which, extrapolated, gave a developmental zero of 14[degree]C, indicating that egg formation is more sensitive to temp, than other stages of the life cycle. The practical life cycle for L. s. is 26-27? days at 25[degree]C; for Cochliomyia macellaria, 16 days. Carbohydrate is essential for continued life of the adult fly and protein for growth of the ovaries and for fertile egg deposition. Casein, Na or ammonium caseinate, blood albumin and Lemco''s beef extract did not allow ovary development. The eggs of old flies are more sensitive to sterilizing agents such as Lysol than are eggs of young flies.