Clipboard, Search History, and several other advanced features are temporarily unavailable. Immunolocalization of antigen via fluorescence requires that Fluorochromes be linked either to the primary antibody (direct method) or to a second antibody (indirect method) to provide a fluorescent signal to mark the site of antibody-antigen binding. Of these two methods, the indirect technique is generally more useful and practical. Fluorochromes can be covalently conjugated to antibodies through reactions with thiol or amine groups. Typically, fluorochromes containing isothiocyanate, succinimidyl ester, or sulfonyl chloride reactive groups are conjugated to amines on the antibody molecules. Provided are step-by-step instructions for conjugating isothiocyanate derivates of fluorescein and sulfonyl chloride derivatives of rhodamine to the amine groups of antibodies. Sotgiu G, et al. J Org Chem. 2007 Jun 22;72(13):4925-31. doi: 10.1021/jo070488n. Epub 2007 Jun 1. J Org Chem. 2007. PMID: 17539686 Flanagan JH Jr, et al. Bioconjug Chem. 1997 Sep-Oct;8(5):751-6. doi: 10.1021/bc970113g. Bioconjug Chem. 1997. PMID: 9327141 J Mol Recognit. 2002 Sep-Oct;15(5):311-20. doi: 10.1002/jmr.593. J Mol Recognit. 2002. PMID: 12447909 Barbarella G. Chemistry. 2002 Nov 15;8(22):5072-7. doi: 10.1002/1521-3765(20021115)8:223.0.CO;2-M. Chemistry. 2002. PMID: 12412057 Davidson RS, et al. Photochem Photobiol. 1990 Aug;52(2):431-8. doi: 10.1111/j.1751-1097.1990.tb04200.x. Photochem Photobiol. 1990. PMID: 2217553 Elledge SK, Tran HL, Christian AH, Steri V, Hann B, Toste FD, Chang CJ, Wells JA. Elledge SK, et al. Proc Natl Acad Sci U S A. 2020 Mar 17;117(11):5733-5740. doi: 10.1073/pnas.1920561117. Epub 2020 Mar 2. Proc Natl Acad Sci U S A. 2020. PMID: 32123103 Free PMC article. Zhang X, et al. Curr Org Chem. 2013 Mar 1;17(6):10.2174/1385272811317060004. doi: 10.2174/1385272811317060004. Curr Org Chem. 2013. PMID: 24363605 Free PMC article.