A series of dye conjugates of goat anti-mouse IgG, streptavidin and other proteins, including R-phycoerythrin (R-PE) are prepared by standard means (Haugland et al., METH. MOL. BIOL. 45, 205 (1995); Haugland, METH. MOL. BIOL. 45,223 (1995); Haugland, METH. MOL. BIOL. 45, 235 (1995)) using Compound 42 and a succinimidyl ester derivative of CY-5 dye.