Antibodies to specific parasites may be readily detected in eluates of dried bloodstains. The method is based upon the reaction of a serum antibody with an antigen on a microscope slide. The presence of a positive reaction is visualized by fluorescence microscopy after reacting the antigen-antibody complex withfluorescein-labelled anti-human immunoglobulin. The frequency of antibodies to five antigens in a random sample of bloodstains has been obtained and the Discriminating Power of these five alone is found to be better than that achieved by the ABO blood grouping system. Other applications of the technique in forensic biology are briefly discussed.