Communication: When activated with TsCl/dimethylformamide/pyridine in the presence of lithium, ammonium, or phosphonium salts, activated terephthalic acid of difficult solubility in pyridine became soluble. Depending on the kind and amount of the salt, terephthalic acid reacted smoothly with 3,3'-dimethyl bisphenol A to yield the corresponding polymer having high molecular weight. However, this reaction could not be successfully applied to the preparation of polyesters from other dicarboxylic acids of difficult solubility.