Thermal field-flow fractionation (ThFFF) is shown here to be capable of isolating the polymeric and rubber particulate components of acrylonitrile-butadiene-styrene (ABS) plastic in a simple analytical procedure. To facilitate the separation, the ionic strength of the two carrier liquids used here (THF and DMF) was brought up to 0.10 mM to increase the retention of the rubber particles. At a field strength (temperature drop) Delta T of 50 K, the two components were well separated, although the polymer component was not completely resolved from the void peak due to its low molecular weight. To facilitate a more rapid separation of the components, both field programming and high flow-rate conditions were examined in some detail. Both the particle-size distribution (PSD) of the rubber particles and the molecular weight distribution (MWD) of the polymer components were obtained using ThFFF. Measured MWD and PSD agreed favorably with PSD determined by dynamic light scattering and MWD obtained by size-exclusion chromatography.