The original histomorphological diagnoses in a series of 34 mycotic lesions from 23 patients with haematological malignancies were re-evaluated by immunohistochemistry. A panel of antibodies was used to identify the agents of aspergillosis, candidosis, fusariosis, scedosporiosis (pseudallescheriosis), and zygomycosis. Apart from improving the diagnosis of aspergillosis, candidosis, and zygomycosis, the application of immunohistochemistry also disclosed three lesions of aspergillosis which had been overlooked during the original screening. It is concluded that the use of immunohistochemistry for the diagnosis of common opportunistic mycoses will not only increase diagnostic specificity, but will also reveal more tissue infections than the conventional histomorphological examination of traditionally stained sections.