The human proto-oncogene BCL-6, encodes transcriptional repressor that is necessary for germinal-center formation, T cell dependent antibody responses, regulation of B cell differentiation, and B-cell receptor signaling modulation. High expression of BCL6 is detected in GC B cells, but not in pre-GC B cells or in more differentiated memory or plasma cells. It performs a function as a potent transcriptional repressor of various target genes, but the precise function of BCL6 in these processes is unclear. In B cell lymphomas, structural alterations of the BCL6 promoter region, including chromoso- me translocation and somatic hypermutation present the most prevalent genetic lesion, especially in diffuse large cell lymphoma. BCL-6 is suggested as an important factor in lymphomagenesis.