Following Fibrin Plate Method of SZOLLOSY and RENGEI² , and ASTRUP and MULLERTZ³, the author conducted a series of experiments in an attempt to identify human blood by detecting the proactivator believed to be one of the enzyme proteins contained abundantly in human blood. As the results it has been found that with 0.1 mg. % SK-solution human blood alone responds to the reaction, showing almost absolute species-specificity within 4 hours but not with blood of monkey. In addition, the sensitivity is so high that it responds positively up to the dilution of 1: 8,000 to 1: 10,000 (human blood: physiological saline solution). By means of this method using 0.1 mg% SK-solution it has been clearly demonstated that the identification of human blood is possible in a variety of conditions and states as may be encountered in practical legal medicine such as with blood stains in cloth, wood, stone, leaves of tree even with a trace of blood stain, old human blood stain left standing for 20 to 30 years, old blood mixed with iron rust, blood stains soaked in various oils, and even the blood stained cloth washed thoroughly and left standing in room temperature for 6 months. Therefore, this Fibrin Plate Method seems to be the excellent one for the identification of human blood.