Graft copolymerization of mixtures of acrylonitrile and methyl methacylate on crumb natural rubber was carried out in toluene at 60degreesC. The nitrogen content of the grafted copolymer was determined by elemental analysis and used to estimate the composition of the copolymer samples. It was found that the amount of acrylonitrile monomeric units incorporated into the polymer was disproportionately lower than the acylonitrile content of the feed and explanations in terms of the e-value of the monomers and the inherent heterogenous nature of the polymerization mixture were offered. The miscibility of the natural rubber-g-polyacrylonitrile-co-poly(methyl methacrylate) with poly(vinyl chloride) was studied by viscometry, differential scanning calorimetry, and phase contrast microscopy. It was found that the natural rubber-g-polyacrylonitrile-co-poly(methyl methacrylate) formed semimiscible blends with poly(vinyl chloride).