Application of colloidal iron method to semithin sections of epoxy embedded tissues

Hale's colloidal iron reaction for acid mucopolysaccharides was applied to semithin sections of Epon-embedded tissues routinely processed for electron microscopy. The reaction was found to be positive only after partial removal of the resin in NaOH/absolute ethanol solution; its sensitivity, however, did not reach that obtained in paraffin or frozen sections. The duration of the Epon-removing procedure seems to be crucial for the specificity of staining.