Spray-dried whole bovine blood, dry poultry egg, and a dry milk substitute are the constituents of the artificial diet currently used for mass rearing screwworm larvae, Cochliomyia hominivorax (Coquerel) (Diptera: Calliphoridae). Due to high cost and uncertainty of the commercial supply of spray-dried blood, research was conducted to identify alternative, locally available, inexpensive, dietary ingredients which could reduce cost of rearing and eliminate concerns of short supply. Experimental diets were prepared without blood component and with various ratios of bovine blood or blood cell product and defatted soy flour. Results indicate that spray-dried bovine blood can be replaced by a readily available and less expensive blood cell product. When the quantity of whole dried blood or blood cell component was reduced or removed completely from the diet, the larvae did not feed adequately, resulting in high mortality. Those larvae that survived produced pupae that were of unacceptable quality. When the milk product was replaced by soy flour, pupae were slightly smaller than those reared using the current diet; however, replacement of egg product with soy flour produced even smaller pupae. Longevity of adult flies that emerged from these small pupae was short and the females deposited few eggs. These results indicate that soy flour cannot replace the blood component from the diet, but can replace the milk product successfully. It is likely that some factor or a combination of factors in the blood act as feeding stimulants, without which larvae are unable to feed normally, resulting in high larval mortality.