The effects of interfacial bulk concentration, pH, ionic strength, temperature, aging and the addition of guanidine hydrochloride, urea and Tween 80 on the interfacial theology of beta-casein solutions have been investigated using an oscillating ring interfacial rheometer. Interfacial tension data are also reported at pH 4.3 and 7.0 and at bulk concentrations of 0.001 to 1% w/v. The Wilhelmy plate method was used for the interfacial tension studies.