The techniques of optical rotation, viscosity, ultracentrifugation, electrophoresis, and solubility have been used to study the effect of heat treatment on the properties of ovalbumin in aqueous solutions of pH 5.5, 7.0, and 8.5. The results have been considered as they relate to the possible sequence of events in any denaturation experiment; nativeequilibriumdenaturedright arrowaggregated. The monomeric form of the protein which remains after heating has been characterized by viscosity and sedimentation measurements and has been found to be hydrodynamically equivalent to the native protein. No evidence for the existence of a denatured monomeric form of ovalbumin in heated solutions has been found. Aggregation of the protein has been found to be rapid and extensive with heating over this pH range. The sedimentations constants of the aggregated form were dependent upon the pH (decreasing with increase in pH) and the ionic strength (decreasing with salt concentration) at which the aggregate was formed. The aggregation of the protein gave rise to increases in viscosity and turbidity which were also dependent upon pH (increasing less at higher pH). The aggregated protein has an electrophoretic mobility at pH 7.0 and 8.5 greater than that of the original protein.