Peripheral blood and bone marrow were studied in 46 patients suffering laryngeal cancer. Two schedules of radiotherapy with and without local hyperthermia were used. Complex hematologic study included electron microscopy of the bone marrow. Apart from general hematologic parameters, partial erythro- and granulocytograms of the bone marrow, mitotic index of karyocytes and morphologic anomalies of erythrokaryocytes were studied. Hematologic studies were conducted both before and after a course of radiotherapy. Adverse effect of hyperthermia and radiation therapy on cells of the granulocytic and immunologic component of hemopoiesis was established.