Heating of aqueous soybean globulin dispersions (concentrationgreater than8per thousand) activates the protein sol to the progel state which is characterized by a marked increase in apparent viscosity measured at the ambient temperature of the progel. The gel is obtained by cooling the progel, and an additional increase in apparent viscosity is observed. The transition is reversible, and the gel can be converted to the progel state by heat and then cooled again to obtain the gel. The progel and the gel are converted by excess heat or the action of chemical reagents to a metasol which does not forma a gel on cooling. The effects of pH, temperature, and ionic strength on the formation of both the progel and the gel are very pronounced. Both the strength and maximum temperature of formation of the progel and gel are affected by pH. The bonds involved in the sol-progel and progel-gel transition appear to be primarily of noncovalent nature.