Alexa Fluor 568 F(ab')2 fragment of goat anti—rabbit IgG is labeled with our superior, red-fluorescent Alexa Fluor 568 dye and is prepared from antibodies that have been adsorbed against pooled human serum, mouse serum, mouse plasmacytoma/hybridoma proteins and purified human paraproteins to minimize crossreactivity. Conjugates of F(ab')2 fragments are sometimes preferable to whole antibody conjugates for secondary detection, since the absence of the Fc region in F(ab')2 fragments prevents interactions with Fc receptor-bearing membranes.