Hematological malignancies encompass a wide variety of diseases. To a certain extent the same basic method can be used to prepare chromosomes from all these diseases, largely because they all yield singlecell cultures relatively easily. Nevertheless, the fact that the different malignant cells have different properties is reflected in the differential success of their chromosome preparation; the acute myeloid leukemias are now relatively well understood and, in general, give fairly consistent results. The acute lymphoid leukemias still have major problems with the quality of the abnormal chromosomes, and some diseases, such as Hodgkin’s disease, still do not have reliable methods to produce any abnormal metaphases.