The carbonyl groups in eight high-performance polyaryl-etherketones and -thioetherketones were reduced to methylene linkages in high yield by treatment at room temperature with triethylsilane in a mixture of trifluoroacetic acid or methanesulphonic acid with either dichloromethane or chloroform. When the starting polyketone is readily-crystallizable, the reduced polymer also tends to crystallize during workup. Amorphous polyketones likewise give amorphous reduction products. The methylene-bridged polymers in general have significantly lower melting points and/or glass transition temperatures than their parent polyketones.