Histone acetylation affects chromatin structural organization, thus regulating gene expression and DNA-related cellular events. Levels of histone acetylation are tightly modulated in normal cells and frequently altered in tumors. Consequently, histone deacetylase inhibitors are currently being tested in clinical trials as anticancer drugs. Presented here is a protocol for measuring the degree of cellular histone tail acetylation, alone or in combination with DNA content to simultaneously evaluate cell ploidy and/or cell cycle progression. The procedure can also be employed to stain peripheral blood samples in order to assess mean histone acetylation levels in patients treated with histone deacetylase inhibitors.