Genetic alterations in the pathogenesis of haematological malignancies may act by two general mechanisms. The first mechanism involves structural alterations of normal genes with the generation of novel genes, the protein products of which act on the host cells to induce the characteristics of malignancies. This may be due to fusion of these genes to other genes with the formation of chimeric genes, or mutations of these genes. The second mechanism involves the inactivation or deletion of genes （tumour suppressor genes or antioncogenes）, the proteins of which suppress malignancies. Investigations of the genetic alterations in haematological malignancies are important in many aspects. Firstly, these mechanisms illustrate important principles in molecular oncogenesis. Secondly, the knowledge of these genetic alterations allows rapid and accurate diagnosis to be made. Thirdly, these molecular changes can be used to formulate methods for detection of minimal residual disease. Finally, they may be targets of treatmen.