This highly cross-adsorbed Alexa Fluor 633 goat anti—guinea pig IgG is labeled with our superior far-red—fluorescent Alexa Fluor 633 dye and is prepared from affinity-purified antibodies that react with IgG heavy chains and all classes of immunoglobulin light chains from guinea pig . To minimize crossreactivity, it has been adsorbed against bovine, chicken, goat, hamster, human, mouse, rabbit, rat and sheep sera prior to labeling. Fluorescence of this long-wavelength Alexa Fluor dye is not visible to the human eye but is readily detected by most imaging systems.