The authors reported some data on the frequency and spectrum of mycotic infections in 76 adult patients with different types of acute leukemia over the last 3 years. The growth of fungi of various species was noted in 50 (23%) of 213 bacteriological tests, candidomycetes being the most common type. Three patients with aspergillosis were described in detail, in 2 of them intravital diagnosis was established. One of these patients with a complete response received amphotericin B therapy despite the fact that acute leukemia in this case was refractory to therapy. The other patient died of profuse pulmonary hemorrhage. The main nosological types of systemic mycoses, their clinical picture, prevention, therapy and characteristic features in acute leukemias were under consideration.