Methylation of some genes is associated with tumoral progression in numerous cancers. The short arm of chromosome 11 is a hot spot for such methylations. The calcitonin gene (11p15) seems to be a good marker of these phenomenons, particularly in acute leukemias. The abnormal methylation pattern of the calcitonin gene in leukemic cells is visualized by Southern blotting after digestion of tumoral DNA with isoschizomeric restriction enzymes which are methylation sensitive or not. These studies seem of interest for acute myeloblastic leukemias (AML) where few molecular markers are available. Moreover hypermethylation of the calcitonin gene correlates with acceleration and transformation of chronic myeloid leukemia (CML). Sequential studies are warranted to evaluate if such techniques might help, especially for timing of bone marrow transplantation in CML.