Soy-derived proteins (soy protein isolate, glycinin, and beta-conglycinin) and bovine whey-derived proteins (whey protein isolate, alpha-lactalbumin, beta-lactoglobulin) were hydrolyzed using subtilisin Carlsberg, chymotrypsin, trypsin, bromelain, and papain. The (in)solubility of the hydrolysates obtained was studied as a function of pH. At neutral pH, all soy-derived protein hydrolysates, particularly those from glycinin, obtained by hydrolysis with subtilisin Carlsberg, chymotrypsin, bromelain, and papain showed a stronger aggregation compared to the non-hydrolyzed ones. This increase in aggregation was not observed upon hydrolysis by trypsin. None of the whey-derived protein hydrolysates exhibited an increase in aggregation at neutral pH. The high abundance of theoretical cleavage sites in the hydrophobic regions of glycinin probably explains the stronger exposure of hydrophobic groups than for the other proteins, which is suggested to be the driving force in the aggregate formation.