A role for histone acetylation, which can alter the accessibility of DNA to transcriptional regulatory proteins and contribute to gene expression, in regulating terminal B cell differentiation was investigated in the mature B lymphoma L10A and mouse splenic B cells. Incubation of the L10A cells with the histone deacetylase (HDAC) inhibitors trichostatin A (TSA) and butyrate increased expression of Blimp-1, J chain, and mad genes, decreased expression of c-myc and BSAP/Pax-5 genes, increased the expression of surface CD43 and Syndecan-1, and decreased surface IgM. Incubation of splenic B cells with TSA and dextran conjugated anti-IgD Ab increased Blimp-1 gene and Syndecan-1 surface expression. The alteration in gene expression and cell surface markers was consistent with induction of the onset of terminal B cell differentiation. Co-incubation of L10A cells with TSA and cycloheximide (CHX) abrogated the up-regulation of Blimp-1 expression, indicating that TSA-activated Blimp-1 expression required synthesis of a transcriptional activator. In contrast, mad expression was increased in L10A cells cultured with TSA and cycloheximide or cycloheximide alone, suggesting mad expression may occur independent of Blimp-1 expression and is regulated by a labile, HDAC associated transcriptional repressor. The results demonstrate that histone acetylation regulates transcription of genes controlling terminal B cell differentiation.