In the prognosis of aplastic anaemia, bone marrow biopsy displays several data which were unknown by the myelogram: quantitative evaluation of marrow cellularity; vascular and mesenchymatous lesions; extension of lymphoid or histiocytic infiltration. Nevertheless, the confrontation and value of these signs with the previously used prognosis data issued from clinical and haematological observations is still discussed. The lack of a clear understanding of the bone marrow failure delimitation is perhaps the reason of these differences. We present the histological results of a cooperative protocol concerning 350 cases of bone marrow failure with 220 first bone marrow biopsies examined in triple blind and confronted in a statistical comparison with the mortality in the first 20 months. We evidence the early unfavourable character of oedema and reticulin lesions: and the unconcerned character of cellularity, and lymphocytic and plasmocytic infiltration. These data must be taken into account in an allograft decision.