The effects of bonding temperature and contact time on autohesive strength development in thermoplastic polysulfone resin and graphite-polysulfone composites were investigated. Two test methods were examined to measure autohesion in the neat resin samples. These included an interfacial tension test and a compact tension fracture toughness test. Auto hesive strength development in fiber-reinforced composites was measured using a double cantilever beam interlaminar fracture toughness test. The results of the tests were com pared with current diffusion theories explaining crack healing and welding of glassy polymers. Discrepancies between the results of the present investigation and the diffusion theories are discussed.