A new procedure is described for dyeing polymer beads using liquid carbon dioxide as a plasticizer to facilitate transport; of dye into the particle phase. Aqueous latexes consisting of monodisperse polystyrene particles with surface-grafted poly(N-vinylpyrrolidone) were dyed with Sudan Red 7B using CO2 at 25 degrees C and 310 bar. Adding CO2 to the headspace above the latex resulted in some dyeing of the polymer, but better results were obtained by forming an emulsion of CO2 in the aqueous latex phase. Emulsions were formed with both a fluorinated and a hydrocarbon-based surfactant. It was found that the carbon dioxide emulsion greatly enhances the transfer of dye into the polystyrene without altering the size or morphology of the particles.