Immunohistochemistry has proved to be a powerful tool for the accurate diagnosis of a number of important mycoses in humans and animals, such as aspergillosis, candidosis, cryptococcosis, blastomycosis, coccidioidomycosis, histoplasmosis capsulati and duboisii, paracoccidioidomycosis, fusariosis, pseudallescheriosis (scedosporiosis), sporotrichosis, trichosporonosis, penicilliosis, and zygomycosis (mucormycosis). These techniques are also applicable to pneumocystosis and to non-mycotic infections caused by algae such as protothecosis. Apart from the specificity of immunohistochemistry, the application of fluorochromes is highly effective for the localization of typical or atypical fungal elements in lesions with only few organisms present. Occasionally, a dual aetiology of fungal infections may be suspected on the basis of morphological study, and dual staining techniques have the capacity for resolving this question by simultaneous and differential staining of two fungal species present in a tissue specimen.