Abstract: Compositions comprising a poly(aryl ether ketone) having intimately dispersed therein, from about 0.1 to 5% sulfur, by weight, based on the weight of poly(aryl ether ketone), the sulfur present as at least one member of the class consisting of elemental sulfur, aliphatic and aromatic dithiols, polysulfides of the formula --R--S--S-- where R is a bivalent aliphatic or aromatic radical, and inorganic sulphides are useful because of their high tensile modulus, high-temperature adhesive properties, and dimensional stability. In a further embodiment the composition further contains a reinforcing filler such as glass or carbon fibers. In further embodiments the composition may be made into fibers or used as adhesives.