A method is outlined for the calculation of azeotropic compositions in ternary copolymerization. The results of these calculations are consistent with those reported by Tarasov et al. (2), and with those calculated by a recent method developed by L. J. Young of the Dow Chemical Company. Our results are further checked with the calculated monomer/copolymer composition during the predicted azeotropic copolymerizations. It was found, in all cases, that the monomer/copolymer composition stays constant, as expected. A method of graphical extrapolation is introduced for estimating the azeotropic composition when some reactivity ratios are inaccurate.