Bone marrow scintigrams (BMS) have been performed in 101 women with histologically proven breast cancer (36 stage IV among them at the time of the first investigation, follow-up examinations available in 41, disease evolution observed in 17). They have been compared to conventional bone scintigram (CBS) as well as to radiological, clinical, biological and follow-up data obtained in the same patients. Only three (7.4%) out of the 41 patients with radiologically or/and histologically proven skeletal metastasis had normal BMS and 33 had corresponding bone marrow scintigraphic defects (BMS ++). On the other hand, only three patients of the 32 with normal BMS had documented skeletal abnormalities. Abnormal bone marrow extension, observed in 61.4% of the patients (62/101), seems to represent a reaction of the reticulo-endothelial system to the disease dissemination - even microscopic - and, as such, to have prognostic implications. As BMS demonstrated skeletal invasion earlier or more precisely than CBS in ten cases, the technique appears of value and of interest in breast cancer management.