Bone marrow was simultaneously obtained by aspiration and by biopsy in a series of 200 patients in order to evaluate the potential usefulness of pathological-anatomical examination (paraffin-embedding technique). Conditions studied included search for lymphomas (26.5%), multiple myelomas (24.5%) and metastases (7.5%) and the evaluation of myeloproliferative syndromes (17.5%) and other hematological disorders such as cytopenias, anemias and leukemias (24%). In 76% of the cases the two methods of evaluation were equivalent. Nevertheless, comparison of the cytological and histological methods provided a greater measure of diagnostic confidence. In 24 cases (12%) the bone biopsy was the only diagnostic procedure; these comprised partly dry aspirations and partly bone marrow smears in which the specific lesion was not represented. Bone marrow aspiration proved superior in 24 cases (12%) in view of the better detection of small and discrete malignant infiltrates and more detailed analysis of blasts and cytological changes in cell maturation. On the basis of the techniques employed in this series of 200 patients, a combination of the two investigations appears to be indispensable for the evaluation of lymphoand myeloproliferative syndromes, of cytopenias with or without fever of unknown origin, and in the search for metastatic disease.