The composition and several of the physical properties of membrane-processed whey protein concentrates (WPCs) were used to develop a model which predicted the strength of the heat-induced gels formed by the WPCs. The compositional factors and physical properties determined were: gel strength; processing pH; ash; total and free sulfhydryls; protein distribution; fat; calcium; phosphorus; protein hydrophobicity; and soluble protein. The best model (R2= 0.93) was one which included protein hydrophobicity as measured by heptane binding and the calcium content with both variables being equally important. Sulfhydryls did not vary enough to be good gel strength predictors.