Normal hematopoiesis is known to be disrupted in hematological malignancies. As research advances, many new treatment techniques are introduced, among which allogeneic transplantation is the most effective. In patients who undergo such treatment, different hematopoietic chimeric states may result which can be detected by indirect analyses using DNA polymorphisms. MRD (minimal residual disease) describes leukemia cells present at a level below that is detectable by conventional means. The detection of MRD has gained special significance in transplantation patients. The detection of fusion transcripts that are generated by chromosomal rearrangements in various hematological malignancies is the direct and the most powerful approach for the detection of MRD. It not only has a prognostic significance but also has a diagnostic importance for patients who have not taken any treatment. The aim of this thesis is the development of PCR-based tests for the diagnosis and monitoring of patients with different hematological malignancies. Therefore the chimerism status of 22 recipient-donor pairs have been evaluated by PCR amplification of STR and VNTR polymorphisms followed by polyacrylamide gel electrophoresis and silver staining. In addition, 44 patients with acute and chronic leukemias have been analyzed for the detection of fusion transcripts generated by t (9;22) (q34;qll), t (8;21) (q22;q22), t (15;17) (q22;q21), inv 16 (pl3;q22), t (4;11) (q21;q23), and t (1;19) (q23;p23) chromosomal rearrangements with RT-PCR.