BCR-ABL-positivity and chimerism analyzed in PB of five patients relapsing after BMT receiving donor leukocyte infusions. BCR-ABL-PCR of PB samples: (▪), one-step-positivity: one leukemic cell in 10⁴ cells; (╞), two-step-positivity: one leukemic cell in 10⁶ cells; (□), BCR-ABL-PCR-negativity with less than one leukemic cell in 10⁶ cells. VNTR-PCR of PB samples: (•), recipient banding in VNTR-PCR; (◑), chimerism demonstrated by donor and recipient banding in VNTR-PCR; (○), donor banding in VNTR-PCR.