Approximately 12% of histone H2B molecules in mammalian brain contain a modification wherein Asp25 is present as the D-enantiomer, and is mostly linked to Gly26 via the side-chain carboxyl. Here we (1) demonstrate the high specificity of a polyclonal antibody to this modification, and (2) use this Ab to demonstrate that this modification is enriched in brain relative to liver, thymus, and HeLa cells.