Streptavidin conjugates are widely used together with a conjugate of biotin for specific detection of a variety of proteins, protein motifs, nucleic acids and other molecules since streptavidin has a very high binding affinity for biotin. This trFluor Tb-streptavidin conjugate comprises streptavidin (as the biotin-binding protein) with trFluor Tb covalently attached (as the time-resolved green fluorescent terbium label). It is commonly used as a second step reagent for indirect immunofluorescent staining, when used in conjunction with biotinylated primary antibodies. It is a very valuable tool for biotin-streptavidin-based biological assays and tests using TR-FRET platform. A variety of the complementary biotinylated reagents are available from numerous commercial vendors.