In this work, the melt fracture behavior of microfilled polymer melts based on a high-density polyethylene (HDPE) was investigated by means of a capillary rheometer, which operated at constant piston velocity. The microfilled melts examined had the same filler content (10 vol%), but differed for the type of filler (glass beads, discontinuous glass fibers, and talc). The results demonstrated that the presence of rigid fillers influences the melt fracture behavior of the filled melts in a way that is dependent on the type of filler dispersed in the HDPE melt. Opposite effects were induced by lamellar particles of talc and by glass fillers (either beads or fibers): the former promoted flow stability, whereas the latter fostered the occurrence of instabilities of "stick-slip" type. The effects induced by the presence of the glass fillers on the oscillating flow that takes place when "stick-slip" instabilities occur were also analyzed and discussed. POLYM. ENG. SCI., 54:364-377, 2014. (c) 2013 Society of Plastics Engineers