The effect of methyl acrylate content in ethylene-methyl acrylate-acrylic acid (E-MA-AA) terpolymers and acrylic acid content in ethylene-acrylic acid (E-AA) copolymers was investigated in blends of these two materials. The E-MA-AA terpolymer with 8 mol % methyl acrylate was not miscible with any E-AA material no matter what the AA content, whereas the terpolymer with only about 2 mol % methyl acrylate was miscible, at least to some extent, with the E-AA copolymer at high acrylic acid contents. Evidence supporting this conclusion derived from gloss, differential scanning calorimetry testing, and dynamic mechanical measurements. For the E-AA polymer material with the highest acid content, there was a synergistic effect for some properties at low added amounts of E-MA-AA copolymer; the tensile strength and hardness were 10% higher than values for the E-AA copolymer, even though the E-AA copolymer was much stiffer. (C) 2003 Wiley Periodicals, Inc.