2-5. Modified Alkaline Congo Red for Amyloid (Ref 4)

Staining Procedures For Plastic Embedded Tissue
Verified at the Applications Laboratory of the Biomedical Division, Sorvall Microtomes


Congo Red Stock Solution
3.0g Congo red
3.0g Sodium chloride
1000.0ml Alcohol, 80%
Congo Red Working Solution
50.0ml Congo red stock solution
0.5ml Sodium hydroxide, 1%
Filter and use within 20 minutes.
Ammonia Water
Add a few drops of ammonium hydroxide to tap water to raise pH and insure proper staining.
Harris' Hematoxylin
See formula in procedure 2-7, b.


  1. Section tissue at 6m.
  2. Stain in working congo red solution for 10 minutes.
  3. Rinse in distilled water; blot dry.
  4. Stain in Harris' hematoxylin for 10 minutes.
  5. Rinse in tap water for 5 minutes.
  6. Dip in ammonia water until sections turn blue.
  7. Rinse in tap water for 5 minutes.
  8. Rinse in distilled water for 1 minute.

Blow dry.


Amyloid red and shows dichromic metachromasia on polarization
nuclei blue

Warning: Some of the chemicals used for the staining procedures given in this section may be hazardous if misused. For this reason, read and observe all warnings and cautions provided by the manufacturer for each chemical before proceeding with a staining procedure.

Note: In order to prevent sections from loosening from the slides during staining, all sections should be heat-fixed (60C to 100C) to the slides for a minimum of 2-5 minutes prior to staining, preferably at the time the sections are mounted on the slides.

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