The value of routinely including biopsy of the iliac crest in the haematological diagnostic programme in medical departments of haematology is elucidated by analysis of 129 biopsies. At the same time, imprints of the biopsies and aspirate smears were compared as regards diagnostic efficacy, which proved 15% greater for imprints and biopsies. The frequency of an inadequate bone biopsy was 7.7%, often because the biopsies were less than 5 mm in length (16%). The individual categories, bone biopsy, imprint, and aspiration smears were of equal diagnostic efficacy in 76%. Guidance for the haematological diagnosis was obtained in 80% of the cases. The incidence of dry tap was 1.6% and the complication rate 1.6%. The optimal result, viz. sufficiently long biopsies (54% over 10 mm in length), is obtained by taking the biopsy with a conically tipped needle (the Jamshidi or Schaadt-Fischer needle) and by making imprints before embedding the biopsies in methacrylate JB IV. The preparation and safety measures in embedding in JB IV and subsequent special staining, including cytochemical studies, are described. By the technique used, it is possible, with some practice, to obtain adequate biopsies in 80-90% of all patients and to take a biopsy and perform aspiration in one session. The patient's position, lying on his side, seems to make him less apprehensive.