This experimental study examines the evolution of the extent of dissolution of the active pharmaceutical ingredient (API) indomethacin (INM) into the polymer excipient Eudragit E PO (E PO) on four screw configurations processed in an APV 15 mm corotating twin screw extruder. The screws were pulled out and quenched by water, which allowed for quick access to the processed stream carcass. Polarized light microscopy (PLM), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FT-IR), were employed to investigate the evolution of INM's dissolution into the molten excipient along the extrusion direction. The FT-IR results show that kneading blocks accelerate the complete dissolution process. The unique capability of fully filled kneading blocks in mixing and melting associated with the dissolution of API into polymeric excipient matrix was discussed. (C) 2011 Wiley Periodicals, Inc. Adv Polym Techn 31: 331342, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.20256