The 12th Workshop on "Mechanisms in B-Cell Neoplasia" continues this series of meetings on intriguing new developments in human and experimental B-cell tumors. The integration of knowledge from basic B-cell biology to the clinical problems of multiple myelomas, follicular lymphoma, mantle cell lymphoma and B-CLL present the challenges that were discussed in the meeting. The discussion focusses on: - Cellular components of the "myeloma clone" - Genomic instability in B-cells and B-cell tumors - The CD5 antigen and B1 cells - Regulation of cell cycle and apoptosis - Role of IL-6, BCL-2, BCL-1, myc in B-cell development