The Alexa Fluor 514 goat anti-mouse IgG is prepared from affinity-purified antibodies that bind to IgG heavy chains and all classes of immunoglobulin light chains from mouse. To minimize crossreactivity, it has been adsorbed against human IgG and human serum prior to conjugation. The yellow-green fluorescent Alexa Fluor 514 dye is far superior to fluorescein in both brightness and photostability, and it can be detected with standard fluorescein, Oregon Green dye or Alexa Fluor 488 dye filter sets. By using instruments that collect spectral distribution information, the signal from the Alexa Fluor 514 dye can be distinguished from both the Alexa Fluor 488 and Alexa Fluor 500 dyes.