Bone marrow biopsies have been investigated in 330 cases of Hodgkin's disease totalising 298 patients, out of which 32 with repeated biopsies. Positive biopsies with typical lesions were found in 32% of patients, the majority in stages III and IV (88.6%), rarely in stage I or II (11.4%). Nonspecific lesions were very frequent (75%), either isolated or accompanied by typical lesions. The majority of the positive biopsies were found in patients with lymphocytic predominance and lymphocytic depletion, or in polytreated patients in an advanced stage of the disease. The specific marrow involvement consisted in lymphocytic infiltrations either nodular or diffuse, Reed-Sternberg (R-St) or Hodgkin cells. The lymphocytic depletion is often accompanied by diffuse fibrosis, atypical histiocytes, fibroblasts and R-St cells. Hodgkin typical granulomas are rare. The positive biopsies were associated with nonspecific reactions including hyperplasia of granulopoiesis, megakaryocytes, territories with hyperplasia or aplasia, fibrosis, disruption of sinus walls, oedema, plasmocytosis, necrosis, myelomonoblastic cells, lymphocyte nodes, etc. The bone marrow histology has a prognostic significance.