This highly cross-adsorbed Alexa Fluor 555 goat anti—mouse IgG is labeled with exceptionally bright, orange-fluorescent Alexa Fluor 555 dye (which is spectrally similar to Cy3 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.