The polysaccharide maltodextrin (MD) can provide a low cost alternative to the fractionated dextran for the use with polyethylene glycol (PEG) in aqueous two-phase. two-polymer systems. The physical characteristics of these MD/PEG systems are similar in many respects to dextran/PEG systems. These systems' behaviour was studied at 25 degrees C and local atmospheric pressure (727 mmHg) under several concentration ratios and molecular weights of MD/PEG. Molecular weight of PEG was 1450, 8000 and 10 000; and MD's molecular weight was 2000 and 4000. This paper establishes phase diagram data, subsequently adjusting the NRTL model for the calculation of activity coefficients. The results are satisfactory and show the good descriptive quality of the model. (C) 2000 Elsevier Science Ltd. All rights reserved.423273278