The constituents of blood stains are normal eosinates of the thiazin series of dyes. Methods are outlined for the chemical examinations of blood stains which are based upon the complete reduction of all dye components present in buffered solutions of limited acidity, and the reduction of their thiazin components alone in strongly acid solutions. Chemical analysis should be supplemented by spectrophotometric analysis to obtain the most adequate characterization of the thiazin components of the eosinates.