Secondary antibodies can be conjugated to enzymes such as horseradish peroxidase (HRP) or alkaline phosphatase (AP); or fluorescent dyes such as fluorescein isothiocyanate (FITC), rhodamine derivatives, Alexa Fluor dyes; or other molecules to be used in various applications. Secondary antibodies are used in many biochemical assays  including:
* ELISA, including many HIV tests
* Western blot
* Immunostaining
* Immunohistochemistry
* Immunocytochemistry