In a rare case of follicluar dendritic cell sarcoma, malignant cells were isolated and cultured in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin 4 (IL-4) and tumor necrosis factor alpha (TNF-alpha). After 14 d, 15% of neoplastic cells differentiated into myeloid-dendritic cell-like elements as demonstrated by immunological and functional characteristics. These cells showed the same cytogenetic abnormality of the malignant clone (fluorescence in situ hybridisation analysis performed on CD1a+ cells) and were able to induce allogenic T-cell proliferation in the mixed leucocyte reaction. These data may indicate that antigen presenting capacity could be a functional state inducible in cellular elements which are believed not to be of hemopoietic origin. Further studies are warranted to confirm these findings and to clarify the possibility to use these cells to generate specific anti-tumoral immune responses.