Objective To evaluate the clinical significance of semi-nested PCR in the detection of minimal residual disease after acute lymphoblastic leukemia(ALL) bone marrow transplantation.Methods Sixteen ALL patients were involved in the study designed,to detect IgH and TCRγ monoclonal gene rearrangements.Clonal rearrangements of immunoglobulin heavy chain and T-cell reception(TCR) γ genes were dynamically detected using semi-nested PCR technique.Results 81.2% of the patients were positive in MRD examined by semi-nested PCR before BMT,and the morbidity was significantly decreased to 37.5% 3 months after BMT(P<0.05).There was no significant difference between allo-BMT and auto-BMT morbidity 3 months after the transplantation.Conclusion It seems that the semi-nested PCR method,very highly sensitive and specific in detecting ALLMRD,may be helpful in the purification of bone marrow in auto-BMT pre-transplantation,and has great clinical significance in the evaluation of therapeutic effect.