Immiscible blends were prepared from polyamide6,10 and poly(trimethylene terephthalate) by extrusion with the goal of identifying the phase inversion composition and domain morphology. Broadly, we studied this system to develop new polymer blends with good engineering properties combined with a high bio-based fraction. Earlier work has demonstrated that the polymers are suitable for melt coprocessing. In this work, we sought to bracket the phase inversion composition, to identify any elements of cocontinuity, and to characterize the domain morphology by a traditional and a novel means. After extrusion of a full range of compositions, the morphologies in the 40-60 vol% range appeared to coarsely bracket the phase inversion point and compositions in this range were selected for detailed microscopic examination. High resolution energy dispersive spectroscopy (EDS) was used to differentiate these chemically similar polymers based on the nitrogen content of the polyamide. Results show elements of cocontinuity appearing at the 50 vol% composition. The EDS mapping techniques employed in this work were successful in sharply differentiating the domains of the two polymers. POLYM. ENG. SCI., 2012. (C) 2012 Society of Plastics Engineers