The friction and wear under dry sliding conditions of injection molded blends of Polyetheretherketone (PEEK) and Polyetherimide (PEI) at temperatures from 20°C to 232°C were investigated on a pin-on-disk apparatus. The friction and wear results were correlated to results obtained from dynamic mechanical thermal analysis (DMTA) temperature scans performed on each of the materials. It was found that tan δ peaks corresponding to α transitions occurring in the vicinity of the glass transition temperature (Tg) coincided with catastrophic tribological failure in the case of PEI and the amorphous PEEK/PEI blends. PEEK and the annealed 70% PEEK/30% PEI blend, exhibited marked increases in friction and wear at and above the Tg. The absence of catastrophic tribological failure in PEEK and the annealed 70/30 blend in the vicinity of the glass transition temperature corresponded to a transitions of significantly lesser strength (i.e. lower tan δ peak values) than those observed in PEI and the amorphous blends. Between 90°C and 105°Cfor PEI and 45°C and 70°C for the PEEK/PEI 50/50 blend, severe to mild friction and wear transitions were observed. DMTA results showing secondary tan δ peaks centered at 75°C for PEI and 38°C for the PEEK/PEI 50/50 blend made evident the occurrence of β transitions in these materials. It appeared that a substantial change in ductility associated with these β transitions resulted in the observed transitional tribological behavior.Presented as a Society of Tribologists and Lubrication Engineers paper at the STLE/ASME Tribology Conference in New Orleans, Louisiana, October 24–27, 1993