The effect of added ethanol and (NH4)(2)SO4 on the flux decline index (FDI) of ovalbumin was examined. Using ternary phase diagrams to predict concentration polarization (CP) layer morphology, it appeared that at 4 wt% ethanol, ovalbumin formed a packed bed of hard spheres on the membrane surface, creating a CP layer with a relatively low FDI value. Protein swelling at high (> 12 wt%) ethanol or moderate salt (5 wt%) concentrations produced a structure that was mon compressible and demonstrated moderate flux resistance. At 28 wt% (NH4)(2)SO4, ovalbumin appeared to precipitate on the membrane surface, resulting in a very high FDI. Overall, a good qualitative correlation was obtained between ovalbumin surface morphology and the FDI. These results, as well as those previously obtained for gelatin, indicate that new approaches must be developed for modelling CP layer resistance.