For the carrion-feeding blow flies, a common source of vitellogenic protein are the carcasses that also serve as larval substrates. This attraction continues well after the blow flies have ceased to oviposit on the carrion, and it has been assumed that a decomposed cadaver remains a suitable source for vitellogenic protein; however, this assumption has never been tested. To test this hypothesis, blow flies (Lucilia sericata Meigen) were supplied with either fresh or decomposed beef liver as protein sources for vitellogenesis for 5 d. Both treatments produced identical ovarian development, indicating that decomposed flesh remains a suitable protein source for carrion-feeding blow flies. These results support the theory that virgin flies are attracted to cadavers of advanced decomposition as a source of protein.