The VDJ rearrangement is detectable in CD34⁺/CD19⁺ cells, but not in CD34⁺/CD19⁻ cells. The PCR of the DNA extracted from the different bone marrow subpopulations separated by FACS sorting, but not of CD34⁺/CD19⁻ cells, gave a smear of DNA fragments indicating polyclonality. The PCR results from one representative patient (G.M.) are shown. The presence of amplifiable DNA in all samples was confirmed by the amplification of the normal bcl-2 gene (data not shown). (M), 100 bp DNA ladder; (−), negative control; (MNC), mononuclear cells.