E-cadherin is a transmembrane glycoprotein that mediates Ca2+-dependent intracellular adhesion in normal epithelial cells. E-cadherin levels in serum are known to be significantly elevated in patients with epithelial carcinomas. However, the role of E-cadherin in haematopoietic cells is less clear. In this study, serum E-cadherin levels were therefore determined in patients with acute or chronic leukaemia, malignant lymphoma or myelodysplastic syndromes. Significant elevation of serum E-cadherin levels was detected in patients with haematological malignancies, and between types of acute leukaemias or subtypes of myelodysplastic syndromes, stages of malignant lymphoma, and phases of chronic leukaemia, respectively, compared with those in healthy adult volunteers. These findings suggest that E-cadherin might be expressed in malignant haematopoietic cells and might be useful as a diagnostic indicator in haematological malignancies.