Skip to main content

Fast Red B

Fast Red B


Chemical structure of Fast Red B

Common Name: Fast red B
Suggested Name: Fast red B
Other Names:

Fast red salt B

C.I. Number: 37125
C.I. Name: Azoic diazo 5
Color: Yellow
Solubility Aqueous: 20%
Solubility Ethanol: 20%
Absorption Maximum: 375
Empirical Formula: C17H13N3O9S2
Formula Weight: 467.4


Fast red B is a diazonium salt often recommended for demonstrating enterochromaffin in carcinoid tumors. During the coupling process, an azo dye is formed which is red-orange.


  1. R. D. Lillie.
    Conn’s Biological Stains
    Williams & Wilkins, Baltimore, MD., U.S.A.
  2. Burstone, M.S.
    Enzyme Histochemistry and its application to the study of neoplasms
    Academic Press, New York, NY, USA
  3. Edward Gurr, 1971
    Synthetic dyes in biology, medicine and chemistry
    Academic Press, London, England.