HETEROCHROMATIN is a cytologically visible form of condensed chromatin capable of repressing genes in eukaryotic cells. For the yeast Saccharomyces cerevisiae, despite the absence of observable heterochromatin, there is genetic and chromatin structure data which indicate that there are heterochromatin-like repressive structures(1-2). Genes experience position effects at the silent mating loci and the telomeres, resulting in a repressed state that is inherited in an epigenetic manner. The histone H4 amino terminus is required for repression at these loci(3,4). Additional studies have indicated that the histone H3 N terminus is not important for silent mating locus repression(5,6), but redundancy of repressive elements at the silent mating loci may be responsible for masking its role. Here we report that histone H3 is required for full repression at yeast telomeres and at partially disabled silent mating loci, and that the acetylatable lysine residues of H3 play an important role in silencing.