In the two years following the discovery that blood and other use residues remain on prehistoric tools, three major topics of research have been carried out. First, the time range and burial environments within which blood will remain stable and amenable to study have been greatly extended. Second, the determination of the species of origin has turned from the extraction and crystallization of hemoglobin (Hb) to electrophoretic separation of all the blood proteins and the use of immunochemical techniques, and third, the radiocarbon age of blood residues has been determined using accelerator mass spectrometry (AMS).