PCR for the t(14;18) translocation provides a sensitive device to identify the presence of minimal non-Hodgkin lymphoma (NHL) cell contamination. Previous experiences have demonstrated that despite the limited stage, Bcl-2/IgH+ cells can be found at diagnosis in PB and/or BM of the majority of the patients. After treatment with local radiotherapy confined to the involved lymph node(s) only, disappearance of circulating Bcl-2/IgH+ cells in PB and/or BM was demonstrated in approximately 60% of positive patients. Quantitative PCR demonstrated the feasibility of clearing PB and BM Bcl-2+ cells after local irradiation of the primary site of the disease only when the basal number of lymphoma cells was <1:100 000.