This paper describes a study of the surface properties of poly(ether ether ketone) (PEEK) using a scratch hardness technique. A comparison of the scratch friction and the hardness values determined for amorphous and semi-crystalline PEEK shows that the crystalline polymer is harder. Studies carried out on PEEK treated with chloroform indicate that this organic solvent induces plasticization in PEEK evidenced by a change in the frictional properties and a decrease in hardness. Also, blending PEEK with other polymers, poly(ether imide) (PEI) and polytetrafluoroethylene (PTFE), demonstrates that the degree of crystallinity in PEEK is increased by the presence of such polymers.