Genomic DNA in eukaryotes is tightly packed in the form of a highly ordered chromatin structure. In view of this tight packing, one of the most important questions in biology is how the transcriptional machinery regulates target genes in chromatin. Reversible modification of histones by acetylation is involved in transcriptional activation as well as repression in chromatin contexts. Recent studies with highly purified histone acetylases have provided insights into the mechanisms whereby acetylases contribute to transcriptional control. Furthermore, they suggest the possibility that histone acetylases could play roles in various forms of DNA metabolism as well as in transcription in chromatin contexts.