Larvae of Phormia regina (Meigen) (Diptera: Calliphoridae) were reared, in isolation, upon either lamb's liver or meridic diets that varied in protein- and carbohydrate-content. An artificial diet containing 53% protein (by mass of dry ingredients) resulted in the heaviest P. regina pupae and shortest development time when compared with larvae reared upon lamb`s liver and all other diets. In diets where the concentration of protein was less than that of carbohydrate, the level of carbohydrate became important. In a diet containing 22.6% protein it was neither the diet with the highest (51%) nor lowest (17%) concentration of carbohydrate that adversely affected development. Specifically, an intermediate level of carbohydrate (33.9%) resulted in an extended larval period, together with increased mortality and reduced pupal weights. Larvae reared in groups of 10 on either liver or a diet containing 53% protein were heavier than those reared in isolation. Group-rearing hastened development on liver, but not on the meridic diet. The results are discussed in relation to the nutritional ecology of saprophagous calliphorids.