Provided as a ready-to-use (Phosphate Buffered) diluent diluting primary or link/secondary antibodies and for use as a negative control. Both monoclonal and polyclonal antibodies are stabilized for long-term storage thereby reducing the number of titrations required from concentrated form. Not for antibodies that have been conjugated with peroxidase. In most cases, antibodies diluted in this reagent can be stored for 24 months at 2-8°C. Diluent is subjected to 0.2 micron filtration. pH 7.4