Numerous recently reported determinations of species or genus-specific blood residues by biochemical and immunological testing of prehistoric artifacts appear irreconcilable with expectations of faunal composition based on archaeological data. Blind tests have shown inconsistencies among alternative immunological techniques, and replicative experiments have raised doubts concerning the durability of blood proteins. It is suggested that until blind testing of artifacts from well-defined archaeological contexts demonstrates the accuracy of immunological and biochemical testing, all such results must be treated skeptically.