The specificity of antibodies to histone modifications (or any antigen for that matter) is crucial for obtaining meaningful experimental data. Cross-reactivity to similar modifications at other residues (e.g. H3K27Me3 vs H3K9Me3) or off-target recognition of other modification isoforms (e.g. H3K27Me1 vs H3K27Me3) can seriously compromise the integrity of any study using these types of reagents.