This highly cross-adsorbed Alexa Fluor 647 goat anti—mouse IgG is labeled with exceptionally bright, far-red—fluorescent Alexa Fluor dye (which is spectrally similar to Cy5 dye) and is prepared from affinity-purified antibodies that react with IgG heavy chains and all classes of immunoglobulin light chains from mouse. To minimize crossreactivity, it has been adsorbed against bovine IgG, goat IgG, rabbit IgG, rat IgG, human IgG and human serum.