A highly sensitive method for forensic ABO blood grouping using monoclonal antibodies was developed in combination with an absorption-elution test and an enzyme-linked immunosorbent assay (ELISA). In this method, monoclonal antibodies eluted from bloodstains with the absorption-elution, were determined by ELISA, for detection of ABO blood group substances in bloodstains. This method enabled us to determine blood group substances in bloodstains with high sensitivity about 10 times greater than a usual absorption-elution test and also to handle many samples (32 samples per a ELISA plate) at the same time. Furthermore, changing the heat elution of antibodies to the acid elution permitted automated analysis for ABO blood grouping using BIOMEK 1000 apparatus (Beckman Instrument, California, U. S. A.).