Sulforhodamine B sodium salt (Acid Red 52) is a fluorescent dye. It can be used from laser-induced fluorescence to the quantification of cellular proteins of cultured cells.

Sulforhodamine B (SRB) is frequently used as a membrane-impermeable polar tracer and for cell density determination via cellular protein measurement (cytotoxicity assay). The SRB assay, divided into four steps—preparation of treatment, cell incubation, fixation, and SRB staining and absorbance measurement—permits inexpensive and sensitive manual or semiautomatic screening. It is applied in testing chemotherapeutic drugs or small molecules in adherent cells, evaluating gene expression modulation (knockdown, gene expression upregulation), and studying miRNA replacement effects on cell proliferation.