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General laboratory information for histology and pathology staff, not medical advice and not a diagnostic procedure.
Short answer: what does a GMS stain for?
GMS (Grocott’s methenamine silver, also written Gomori methenamine silver) is a special stain that identifies fungi in tissue sections. Fungal cell walls are oxidized to aldehydes, which reduce silver to metallic silver, so organisms appear black against a light green background. A black organism shows that fungal wall material is present; it does not by itself name the species.
Definition and scope
GMS belongs to the fungal silver impregnation stains within histological staining. Where routine H&E staining can leave fungi faint or invisible, GMS is the stain a laboratory adds to make fungal elements, and the cysts of Pneumocystis, stand out. One published histology manual (University of Utah WebPath, read 2026-11-07) states the purpose of its GMS procedure simply: “To identify fungi.” The method is named for Robert G. Grocott, who in 1955 published a modification of Gomori’s methenamine-silver technique for fungi in tissue sections and smears (history as summarized by Wikipedia, a secondary source).
How it works in practice
Principle
The WebPath manual describes the chemistry in two steps: mucopolysaccharide components of the fungal cell wall are oxidized (chromic acid in that procedure) to release aldehyde groups, and the aldehydes then reduce silver from the methenamine silver solution to metallic silver, which makes the wall visible. Gold chloride toning and a light green counterstain give black fungi on a green background.
Reagents and controls named in the manual
- Section: 10% formalin-fixed, paraffin-embedded, cut at 4-5 µm.
- Reagents: 2% chromic acid; methenamine silver stock (3% methenamine with 5% silver nitrate, kept in a brown acid-cleaned bottle in the refrigerator, stable for 3 months in that manual); 1% sodium metabisulfite; 5% borax; 0.5% gold chloride; 5% sodium thiosulfate (hypo); 0.2% light green.
- Glassware: acid-cleaned.
- Positive control: any tissue containing fungus; the manual prefers a control block made from tissue containing both aspergillosis and Pneumocystis.
The manual is one local procedure card, so treat its concentrations and times as an example rather than a universal standard; follow your own validated procedure or the kit’s instructions for use.
Troubleshooting and hazard checklist
This checklist, drawn from the same manual, pairs each common fault with the check the manual gives.
| Observation | What the manual says to check |
|---|---|
| Chromic acid has turned brown | Change it. |
| Organisms do not turn black | Check that the chromic acid, sodium metabisulfite and borax are fresh. |
| Working silver solution cloudy, or mirroring on the jar | Make a new solution. |
| Tissue falls off the slide in the microwave variant | The manual links this to 5% chromic acid used with the microwave method. |
Hazards in the same manual: chromic acid is corrosive and a carcinogen; silver nitrate is an oxidizer and a severe skin and eye irritant; hot solutions go in a fume hood; wear gloves, goggles and a lab coat.
What GMS shows for specific organisms
The table is drawn from Guarner and Brandt, “Histopathologic diagnosis of fungal infections in the 21st century,” Clinical Microbiology Reviews 2011 (PMC3122495, read 2026-11-07). The review also states that fungal silver impregnation stains cannot alone solve the identification challenges.
| Organism | What the review describes | Stain note |
|---|---|---|
| Candida | Mats of yeasts 3-5 µm across, intermingled with pseudohyphae | Organisms can be seen with H&E, GMS and PAS |
| Cryptococcus | Encapsulated, spherical to oval yeast, 5-10 µm | As with other yeasts, the wall stains with GMS and PAS; the capsule stains with Alcian blue and Mayer’s or Southgate’s mucicarmine, and some yeasts make less capsule |
| Aspergillus | Thin (3-12 µm), septate hyphae with acute-angle (45°) or dichotomous branching | Recognized by this morphology; a silver stain highlights hyphae but does not name the genus |
| Pneumocystis | Foamy material of thin-walled spheres 2-5 µm with an intracystic focus | Shown by GMS |
| Blastomyces | Contour of the yeast | Best highlighted by fungal silver stains such as GMS; on H&E it looks like a space between contents and tissue |
| Sporothrix | Difficult to see on H&E | Use GMS or PAS |
| Coccidioides | Spherules and endospores | GMS highlights spherule walls and endospores; PAS reactivity varies with age |
Limits and false-negative causes
The review notes that fragmentation or necrosis of fungal elements may make GMS faintly positive or negative, and that poor GMS staining of hyphae should suggest mucormycosis. For the laboratory, that makes the stain a screen to read with the H&E and the clinical context, not a stand-alone answer. Related organism groups are covered in what is mycology; for a different special stain with its own organism targets, see acid-fast staining.
Common misunderstandings
- “Black means a specific species.” It means silver was deposited on fungal wall material. Morphology, additional stains and other testing assign the identity.
- “GMS shows capsules.” For Cryptococcus it stains the wall; the capsule needs Alcian blue or mucicarmine.
- “Negative GMS rules out fungus.” Fragmented or necrotic elements, and organisms that stain poorly such as the agents of mucormycosis, can be missed.
FAQ
What does GMS stain for?
Fungi in tissue sections, including yeasts, hyphae and Pneumocystis cysts. The fungal wall is rendered black on a green counterstained background.
What does a GMS stain for Aspergillus indicate?
It highlights hyphae, which the review describes as thin, septate and branching at acute angles. That morphology, read with H&E and clinical information, supports the pathologist’s interpretation; the stain alone does not name the species.
Can Candida be detected with a GMS stain?
Yes. Guarner and Brandt state that Candida organisms, yeasts mixed with pseudohyphae, can be seen with H&E, GMS and PAS stains.
Can Cryptococcus be found in a GMS stain?
Yes, the yeast wall stains with GMS, as it does for yeasts in general. The capsule does not, so Alcian blue or mucicarmine is used to show it.
Sources
- University of Utah WebPath histology staining manual, “GMS – Methenamine Silver – Grocott’s, Modified”: webpath.med.utah.edu/HISTHTML/MANUALS/GMS.PDF (read 2026-11-07).
- Guarner J, Brandt ME. Histopathologic diagnosis of fungal infections in the 21st century. Clin Microbiol Rev. 2011: PMC3122495 (read 2026-11-07).
- Grocott RG. A stain for fungi in tissue sections and smears. Am J Clin Pathol. 1955 (as cited by Wikipedia, “Grocott’s methenamine silver stain”, read 2026-11-07).
