Streptavidin and Conjugates include streptavidin in a purified form, conjugated to enzymes or fluorophores or activated for crosslinking to sulfhydryl or carbonyl groups. These purified and conjugated forms of recombinant streptavidin protein enable detection of biotinylated antibodies and other probes in a variety of standard assay methods, including Western blotting, ELISA, immunohistochemistry and fluorescence imaging. Purified streptavidin and the streptavidin-HRP conjugates (peroxidase-conjugated streptavidin) are supplied lyophilized in phosphate-based buffers for immediate reconstitution with water. Alkaline Phosphatase conjugates are supplied as a liquid in a Tris-based buffer.