Alpha, beta, and gamma conglycinins are soybean globulins which together with glycinin constitute the major components of the reserve proteins of soybean seeds ( Glycine max). These proteins were isolated by fractionation procedures based on Bio-Gel A-1.5m and Sephadex G-100 gel filtration, and DEAE-Sephadex chromatography. The isolated conglycinins were found to be homogeneous by immunoelectrophoresis in agar gel, disc electrophoresis, and disc immunoelectrophoresis. The antisera used for their identification were an anti-soybean water extract serum 123 and a monospecific anti-γ-conglycinin serum 130. In addition, a monospecific anti-glycinin serum 102 was used to detect possible contamination of conglycinin preparations by glycinin. The identity of α-conglycinin with a 2S soybean globulin component, β-conglycinin with the major component of a crude 7S soybean protein preparation, and γ-conglycinin with the major component of another crude 7S soybean protein preparation is discussed.