Which stain is used to differentiate collagen from smooth muscle fibers by staining collagen green and muscle red?

• A. Gomori's One-Step Trichrome Stain
• B. Van Geison's Picric Acid-Acid Fuchsin Stain
• C. Verhoeff's Elastic Stain
• D. Mallory's Phosphotungstic Acid-Hematoxylin

Answer: (A)

The main idea is that this is a trichrome stain designed to differentiate connective tissue from muscle by color. Gomori's One-Step Trichrome uses a combination of dyes so collagen fibers take on a green color while smooth muscle fibers appear red. This distinct color separation makes it easy to see fibrosis, connective tissue proliferation, or tissue architecture where you need to distinguish collagen from muscle. Nuclei are typically stained dark by the hematoxylin component, adding another layer of contrast. Other stains listed have different dye combinations and color outcomes, so they don’t produce the same green collagen and red muscle differentiation.