A series of new poly(arylene ether ketone)s and poly(arylene ether sulfone)s, obtained starting from dihydroxynaphthalene isomers, have been prepared by solution condensation polymerization. The polymers, having inherent Viscosities from 0.20 to 0.77 dl g(-1), have been obtained in quantitative yields, had excellent thermal stability as shown by 10% weight loss temperatures in nitrogen and air (above 460 and 430 degrees C, respectively) and high glass transition temperatures (in the range 151-278 degrees C). X-ray diffraction patterns confirmed the semicrystalline character of some polymers. The location of the naphthalene-ether bond appears to affect the polymer properties.