Histone deacetylases (HDACs) are components of nuclear multiprotein complexes that deacetylate histones and perform important roles in repression of transcription.Using specific rabbit mAbs, we analyzed by immune histochemistry and confocal immunofluorescence analysis the expression and subcellular localization of HDAC1–4 and HDAC9 in sections of adult human third molars. HDAC2 and HDAC9 were expressed in some pulpal cells and strongly expressed in the majority of mature odontoblasts.In contrast, only weak expression of HDAC1, HDAC3 and HDAC4 was observed. Confocal immunofluorescence analysis together with the DNA stain DRAQ5 revealed that HDAC2 and HDAC9 were coexpressed within the odontoblast nucleus, but localized to distinct subnuclear structures.In contrast to the current point of view, HDAC2 is strongly expressed in a terminally differentiated cell type.Our results imply that class I and II HDACs are involved in the transcriptional regulation of human odontoblasts in vivo.