Long-term cultures from bone marrow of patients with chronic myeloid leukemia were obtained. The cultures were characterized by the reduced period of hemopoiesis. The enrichment of the adherent cell layer with endothelial cells or their extracellular matrix was not stimulative. The Ph'(+) malignant cells persisted in culture during the whole period of hemopoiesis. The data obtained indicate that the long-term bone marrow culture system is not suitable for the elimination of malignant cells from leukemic bone marrow.