Oct-2 is a transcription factor of the POU homeo-domain family that binds to the Ig gene octamer sites, regulating B-cell-specific genes. These are involved in proliferation and differentiation and despite the scarce evidence for Oct-2 expression in T cells, it has been shown that this factor participates in transcriptional regulation during T-cell activation. Oct-2 activity is dependent on phosphorylation and alternative splicing, although it seems that the level of its expression can be used as a marker of B-cell lineage and differentiation. Several studies of Oct-2 expression have shown a low-level expression in pre-B, T-cell, myelomonocytic, and epithelial cell lines, whereas all mature B-cell lines display high levels of expression. Analysis of Oct-2 expression in primary Hodgkin’s lymphoma (HLs) and cell lines derived from it showed that the tumor cells analyzed had high levels of expression and activity, suggesting a common B-cell origin for all types of HLs.