Immunological analysis is complementary of morphological analyses in the detection of neuroblastoma BM metastases. It attests the neuroblastic nature of rare pseudolymphocytic isolated cells. The combination of immunocytochemical technique (alkaline phosphate) and double-immunofluorescence technique allows the detection of as few as 10(-5) residual neuroblastoma cells. At the time of bone marrow harvest, it permits a precise evaluation of malignant cells in the graft.