The mRNA expression level of the gene delta-like (Dlk), coding for a signal transducer related to the Delta-Notch family, was measured using real-time PCR methodology in a large series of control biopsies (n = 61) and bone marrow trephines from patients with myelodysplastic syndrome (MDS) (n = 93) and related myeloid disorders (AML, n = 16 and chronic myeloproliferative disease (CMPD), n = 38). It turned out that dlk is strongly overexpressed in a subset of MDS (16%) cases, however with higher frequency in blast rich MDS cases. Therefore, the quantitative detection of dlk mRNA can support the morphological diagnosis of MDS in selected cases.