Conditioned media (CM) from a human lung adenocarcinoma cell line expressing interleukins 1 and 6 (IL-1, IL-6), granulocyte (G), macrophage (M), and GM colony-stimulating factors (G, M, GM-CSF) and transforming growth factor beta (TGF beta) were used to stimulate growth of bone marrow (BM) cells from 18 persons with leukemia, myelodysplastic syndrome, or lymphoma. The objective was to increase numbers of analyzable metaphases and to enhance the likelihood of detecting cytogenetic abnormalities. Although more mitotic cells were observed with CM, the detection rate of cytogenetic abnormalities decreased in 12 of 18 cases. These data indicate that use of CM for cytogenetic analyses may favor growth of normal versus leukemia cells and mask cytogenetic abnormalities.