Carbon-fiber-reinforced PEEK composites (APC 2, ICI pie) were plasma treated for adhesive bonding. This was done in a microwave plasma in argon or oxygen. An epoxy-based film adhesive (AF 191, 3M) was employed for adhesive bonding (1 h curing at 175 degrees C, 30 N/cm(2)). Both plasma treatments resulted in a high level of lap shear strength (Ar: >40 MPa, 25 degrees C). The environmental behaviour (42 d, 70 degrees C hot water) of the adhesively bonded composites has also shown that good bonds could be obtained. Regarding the stability of the freshly-treated surfaces against exposure to the surrounding atmosphere only a small decrease in lap shear strength was observed. After storage for 4 weeks in air the strength was still almost 85% of that when the bonding was done directly after the treatment. ESCA measurements revealed an increase in carbon-oxygen groups by the plasma treatment and a strong cleavage of the PEEK chemical structure.