Blends of polyamide-6 (PA6) or postindustry polyamide-6 (piPA6) and high-density polyethylene (HDPE) or recycled high-density polyethylene (rHDPE) were processed in single and twin-screw extruders. The use of rHDPE in the blends promotes a significant decrease of size domains and improvement in the mechanical properties. The thermal stability was also slightly improved compared with PA6 and HDPE blends. The Molau test exhibited a stable emulsion in formic acid, which can be attributed to the formation of an interfacial copoymer involving polar amino end groups of PA6 and the rHDPE, respectively. These results indicate that recycled polymers can be used in the production of polymer blends with improved properties. POLYM. ENG. SCI., 49:2005-2014, 2009. (C) 2009 Society of Plastics Engineers