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Methylation for the Periodic Acid-Schiff Reaction


For the Periodic Acid-Schiff Reaction

This procedure is used to block acid groups, particularly carboxyl groups. As a consequence, basophilic staining materials cease to be basophilic. Extended treatment destroys Periodic Acid-Schiff (PAS) positivity of some carbohydrates. This may be used as a means of identifying them, particularly if done in conjunction with other blocking procedures.


0.1N Hydrochloric acid, conc.0.83mL


Place dewaxed sections into the solution in a sealed container at the temperature specified for the time given.

Glycogen58°C3 daysComplete
Epithelial mucin58°C3 daysComplete
Glycogen37°C7 daysNot complete
Epithelial mucin37°C7 daysNot complete

It should be noted that methylation is more commonly used to abolish metachromasia or cytoplasmic basophilia. Treatment of sections at 37°C with 1% hydrochloric acid in methanol for 2 days will usually accomplish this, while not affecting PAS reactivity.

Safety Note

Prior to handling any chemical, consult the Safety Data Sheet (SDS) for proper handling and safety precautions.


  1. Lillie, R.D., (1954)
    Histopathologic technique and practical histochemistry Ed.2
    Blakiston, New York, USA