Blends of poly( ether imide) (PEI, Ultem 1000) and an aromatic poly( ether amide) were studied. Although homogeneous or heterogeneous blends can be obtained depending on the blend preparation method, the inherent miscibility of the mixture was finally established. The so-called enthalpy relaxation method was used to detect one or two glass transition temperatures in the blends in spite of the similarity of the pure component transitions. Fourier transform infrared analysis provided additional evidence of the specific interactions, which could be in the origin of the miscibility. A preliminary study of the influence of the homogeneity level in the transport properties of the blend films was also undertaken. Carbon dioxide at 1 bar was used as a penetrant.