In heat denaturation studies conducted in the past the genetic variants of glycinin have been considered as a homogeneous group of proteins. In this work the validity of this assumption was tested. It was found by calorimetric studies that glycinin denatures heterogeneously at pH 7.6. When the temperature of isothermal treatment is increased from 70 to 82 C the proportion of glycinin remaining native progressively decreases from 95␝o 5 hile the denaturation temperature of the glycinin remaining native increases from 88.5 to 95 C. Similar trends were found for pH 3.8. Fractionation and subsequent analysis (MALDI-TOF and CE) of isothermally treated samples demonstrated that at pH 7.6 the heterogeneous denaturation is caused by differences in thermal stability of the genetic variants of glycinin. The stability increases in the order G2/G3/G1< A4< G5 < G4.