Detection of MRD remains one of the major goals in the treatment of acute lymphoblastic leukemia (ALL). We have used the polymerase chain reaction (PCR)-heteroduplex (HD) analysis to assess and confirm the clonal expansion of T cell receptor (TCR) gamma and delta gene rearrangements in 24 T-ALL patients at diagnosis. 52.4% revealed Vdelta1-Jdelta1; 48% Vdelta2-Ddelta3; 62.5% Vgamma1-Jgamma1 and 46% both Vdelta1-Jdelta1 and Vgamma1-Jgamma1 clonal rearrangements. 6/24 patients had TAL-1 deletion. These clonal markers were used to monitor MRD in remission/relapse bone marrow samples for periods ranging from 6 to 75 months after diagnosis. Patients who relapsed and died revealed a continuous PCR-HD positivity in their clinical remission bone marrow samples. HD analysis established identical diagnostic clone at relapse. Patients who are in long-term clinical and morphological remission achieved PCR-HD negativity in their 8-12 months bone marrow remission samples and continue to be PCR-HD negative. MRD monitored in six patients with two diagnostic PCR--HD positive clonal markers reveal an identical pattern ensuring circumvention of false positive and negative results. Thus, we conclude that PCR followed by HD analysis is a useful technique to monitor MRD in remission/relapse samples in ALL patients.