Commercial whey protein concentrate (WPC) products, manufactured by ultrafiltration with and without lactose hydrolysis, were compared for proximate composition, mineral and trace mineral composition and for protein solubility and viscosity parameters. Protein concentration ranged from 30.5 to 52.7%, while ash content ranged from 5.9 to 12.0%. Extent of lactose hydrolysis in lactose-hydrolyzed WPCs was estimated at 60 to 75% of the initial lactose level. Protein solubility of 10% protein dispersions of the WPC samples ranged from 90 to 100% and was not affected by heating WPC dispersions at 65°C for 30 min or by increased centrifugation force in solubility determination from 40,000 × g to 100,000 × g. All WPC dispersions exhibited pseudoplastic flow behavior as indicated by flow behavior indices (n) of less than 1.0. WPC dispersions possessed a low viscosity as indicated by consistency index (k) data, and k values decreased slightly after heating. Lactose hydrolysis had no apparent effect on solubility or viscosity properties of the WPC dispersions. Alteration of electrophoretic mobility of polyacrylamide gel electrophoresis was observed for α-lactalbumin in lactose-hydrolyzed WPC samples.