Abstract: Effects of PEG molecular weight, system polymer concentrations (tie-line lengths), pH and sodium chloride concentration, on the partition coefficient of trypsin in PEG-purified Anacardium occidentale L. (cashew tree) exudate gum polysaccharide aqueous two-phase systems have been investigated. Changes in PEG molecular weight, tie-line length and pH, had relatively little effect on trypsin partitioning, with partition coefficients (Κ) < 0.3, i.e., trypsin partitioned preferentially into the A. occidentale L. gum (lower) phase. However, addition of sodium chloride (0.1 M) resulted in dramatic increases in Κ values with increasing pH using the PEG 4000 (9% w/w)-purified A. occidentale L. gum (18% w/w) system, increasing to 3.70 at pH 7.0 and 9.77 at pH 8.0, i.e., trypsin partitioned preferentially into the PEG 4000 (upper) phase. Relative trypsin activities in the phases were investigated for these systems (with different sodium chloride levels) and high activities were obtained at pH 7.0 (70.9%) and pH 8.0 (90.9%) in 0.1 M sodium chloride, which in conjunction with their Κ values, clearly demonstrates their suitability as lower cost enzyme purification procedures (compared with PEG-dextran).