Global histone modifications and their putative relevance to short and long term cellular programming have drawn substantial interest in the study of chromatin. Here we describe the use of reverse-phase liquid chromatography coupled to Linear Ion Trap-Fourier Transform Mass Spectrometry (RPLC-LTQ-FTMS) to quickly profile post-translationally modified isoforms and variants for core histone proteins from as few as 5x10(4) cells at isotopic resolution. Such LC-MS profiling greatly facilitated the detection of histones from HeLa S3 or 293T cells experiencing shRNA- or siRNA-knockdown of histone deacetylase (HDAC) 1, 2, 3 or 1 and 2 together. In no case was significant global histone hyperacetylation relative to control cells observed, suggesting possible compensation of deacetylation activity by partially redundant enzymes in the 18-member HDAC family. This contrasts sharply with yeast where genetic deletion of HDAC rpd3 causes massive hyperacetylation. Treatment of cells with TSA and class I selective HDAC inhibitors had similar ability to induce global histone hyperactylation, though to different extents in HeLa S3 vs. 293T cells.