To enhance the specific signal obtained with a monoclonal antibody or a polyclonal second antibody conjugated to TRITC. The phenomenon of a weak reaction of a monoclonal antibody is e.g. well known in different analysis of vital peripheral blood mononuclear cells in suspensions by the expression of surface markers. A similar situation exists in solid phase assay systems (ELISA, blotting, DIBA) when used for the identification and /or quantitative determination of minute amounts of soluble specific antigens or antibodies. The sensitivity of the TRITC hapten-anti-hapten system makes it a valuable alternative to the biotin-avidin system. The optimum working dilution is an assay-related characteristic and should always be determined by titration. For histochemical use optimum dilutions are mostly from 1:10 to 1:40, in ELISA from 1:100 upwards, in Western blotting from 1:200 upwards. These data should be interpreted as general recommendations only.