The efficiency of four different compatibilizers melt-mixed with a poly(ethylene terephthalate)/high density polyethylene (PET/HDPE) blend was investigated. The compatibilizers studied were an ethylene-glycidyl methacrylate copolymer (E-GMA), an ethylene ethylacrylate glycidyl methacrylate terpolymer (E-EA-GMA), a hydrogenated styrene-butadiene-styrene copolymer grafted with maleic anhydride (SEBS-g-MA) and a MA-modified ethylene-methyl acrylate copolymer (E-MeA-g-MA). The techniques applied were dynamic mechanical analysis, tensile and impact testing, optical and electron microscopy, thermal analysis and Fourier transform infra-red spectroscopy. On the basis of morphological evidence and tensile testing, which proved most discriminating, the compatibilizing effectiveness was found to decrease in the sequence, E-GMA> E-EA-GMA> SEBS-g-MA>E-MeA-g-MA. These results are explained on the basis of differing reactivities of the GMA vs. the MA functionality contained in these compatibilizers.