Terahertz spectroscopy has been presented as a new technique for analyzing the degree of dispersion of polymeric compounds. It is a contact-free and nondestructive technique that can also be used to monitor the filler content of compounds inline during the extrusion process as has already been presented elsewhere. The utilized terahertz frequency range bridges the infrared and the microwave region in the electromagnetic spectrum. Here, we present offline terahertz measurements and mechanical tests on injection molded specimens consisting of wood plastic composites with varying filler contents and different dispersion qualities. A clear linear relation between results of the terahertz measurements and mechanical tests has been found showing that terahertz spectroscopy is a powerful tool for analyzing polymeric compounding processes. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers