An epoxy resin (Epikote 828), cured with 3-diethylaminopropylamine (DEAPA) was blended with a polyetherimide. The glass transition temperature (T(g)) and information on the morphology of the blend were obtained by dynamic mechanical analysis and transmission electron microscopy, respectively. The critical stress intensity factor (K(1c)) and critical strain energy release rate (G(1c)) based on 3-point bending test data were also measured. The results indicate that the polyetherimide was miscible with the cured epoxy matrix. K(1c)) and G(1c)) decreased with the addition of the polyetherimide.