Abstract: Absorption-inhibition test was carried out to prove that the agglutinin existing in anti-human hemoglobin precipitin serum is essentially anti-human red blood cell agglutinin. We used this agglutinin to identify the species of unknown bloodstains by elution test. The minimal identifiable amount of bloodstain corresponds to 0.001 ul of fresh blood; 448 cases of human bloodstain kept for less than 11 years showed correct reaction; 33 out of 52 cases of human bloodstain kept for 12～16 years showed positive result and the remaining 19 cases negative; all the fresh bloodstains of 15 species of animal showed negative result.