Cultural, ultrastructural, cytochemical and histological investigations of bone marrow tissue were conducted in 26 patients with varying types of preleukemia states. A number of early structural, morphological and functional signs of hemopoietic disorders of different character and manifestation degree have been revealed. Particularly, a relationship has been established between the pathologic changes appearing in the bone marrow stroma and disorders in the morphological and functional state of the hemopoietic cells.