Monte Verde, a habitation site in southern Chile, is the source of exceptionally well-preserved organic materials. The depositional and chemical circumstances that led to the persistence of this unique assemblage included an anoxic, reducing environment protected by an overlying peat layer and a silica gel-rich substrate. Utilizing the immunological techniques of ELISA assays and Western blots, a subset of lithic artifacts was tested for blood traces. Geochemical analysis of the soil matrix provided the necessary comparative data for assessing the biological etiology of the residue extracted from these tools. One tool was found to be positive for hemoglobin, and was convincingly above both the chemical and geological background of the immunological assays. These findings complement the archaeological interpretation of the site.