Autologous bone marrow transplantation is now a major tool in the treatment of human leukemias and lymphomas. Evaluation of residual disease by standard cytological methods is difficult. Cytogenetics provide clonal markers which are specific features of leukemic cells. Detection of minimal disease by chromosomal methods is possible in acute leukemias, it requires karyotyping of a few hundred metaphases from a short term culture. A preselection of the material to be examined will improve the degree of sensitivity of the method.