Pneumocystis jiroveci is one of the major microbial pathogens associated with opportunistic pulmonary infections in patients receiving immunosuppressive therapy or with immune deficiencies. Presently, the most common means to diagnose Pneumocystis jiroveci infection is by microscopic detection of the organisms in specimens such as bronchoalveolar lavage, open lung biopsy tissue, induced sputum and transtracheal aspirate. A variety of histochemical stains have been used to detect Pneumocystis in clinical specimens. These histochemical stains include the Diff-Quik, Grocott-Gomori methenamine silver (GMS), and Calcofluor white stains. ... GMS stain is a silver precipitation stain commonly used to visualize fungi in histologic sections.