A program of blood residue analysis at Çayönü Tepesi in southeast Turkey was undertaken from 1984 to 1987. The research began as an investigation of the feasibility of detecting and identifying blood residues in a field setting with subsequent additional analyses and verification in the laboratory. Field and laboratory techniques included Labstix detection of hemoglobin. The identification of species was done using hemoglobin crystallization. Immunological techniques were used in the laboratory to verify the identification of blood. Research centered on material from the skull building where the blood of <i>Bos primigenius</i> (the extinct progenitor of modern cattle), sheep, and goat were found in addition to human blood. The conjunction of animal and human blood in a structure where more than 90 human skulls as well as complete and partial skeletons were interred suggests some yet-unknown ritual mortuary function.