Isoimmune monospecific agglutinating antibodies reacting with an eryth
rocyte antigen, designated Aba, were obtained by immunizing Siberian s
turgeons with allogenic erythrocytes. This antigen was detected in 65.
2% of sturgeons studied. Serum samples taken from intact sturgeons con
tained no natural isohemagglutinins. A modification of a two-stage pro
cedure was developed to prevent erythrocytes from forming a jellylike
substance during enzymatic treatment.