[Value of immunological investigations in a difficult diagnosis of acute lymphoblastic leukaemia (author's transl)].

A 9-year-old child was found to have massive invasion of his bone marrow by malignant cells. Experienced pathologists were unable to determine on morphological grounds the nature of these cells, even after electron microscope study and multiple cytochemical staining of bone marrow smears. However, serological analysis of the cells showed that they displayed an antigen specific to cells from common acute lymphoblastic leukaemia HLA-DR antigens and contained high concentrations of terminal deoxynucleotidyl transferase. A course of the chemotherapy usually prescribed for common acute lymphoblastic leukaemia resulted in complete remission.