Cetylpyridinium Chloride as a Fixative for Glycosaminoglycans in Histologic Sections

To the Editor.—  Matsuoka et al¹ wrote approvingly of cetylpyridinium chloride (CPC) as a glycosaminoglycan (GAG) fixative in histologic sections, confirming other opinions quoted in their letter to the editor recently published in the Archives. Whatever the practical advantages of CPC (and they are clearly real), I would like to sound a strong cautionary note.I introduced CPC in 1955 as a precipitant for polyanions, including GAGs (see Scott² for a review), and shortly thereafter it was used in histology by Williams and Jackson³ as a fixative, usually together with formaldehyde, and, equally significantly, as a blocker of uptake of cationic dyes by Geyer.⁴ In the latter role, the organic cation occupies the binding sites that cationic dyes would occupy in staining the substrate. The blockade is stable and permanent; it cannot be reversed by, for example, simple washing with water. The blockade could be made