1-(2-Carboxyethyl)pyrrole has been copolymerized with pyrrole in the presence of silica particles to produce stable colloidal dispersions of polypyrrole copolymer-silica microparticle’s containing carboxylic acid groups. These new dispersions have been extensively characterized in terms of their particle size and chemical composition by transmission electron microscopy, disk centrifuge photosedimentometry, elemental microanalyses, thermogravimetry, and both FTIR and visible absorption spectroscopy. The presence of the carboxylic acid groups at the surface of the microparticles has been confirmed by X-ray photoelectron (XPS) spectroscopy. Visible absorption spectroscopy studies confirmed that the optical absorbance of these carboxylic acid-functionalized polypyrrole-silica microparticles is up to 4 times higher (at a wavelength of 400 nm) than a commercial dyed carboxylated polystyrene latex (Polymer Laboratories’ SuperCarboxyl Hi-Dye) of the same solids concentration. Thus these conducting polymerbased microparticles are expected to have biomedical applications as novel "marker" particles in immunodiagnostic assays.