The induction of immediate-early (IE) genes, including proto-oncogenes c-fos and c-jun, correlates well with a nucleosomal response, the phosphorylation of histone H3 and HMG-14 mediated via extracellular signal regulated kinase or p38 MAP kinase cascades. Phosphorylation is targeted to a minute fraction of histone H3, which is also especially susceptible to hyperacetylation. Here, we provide direct evidence that phosphorylation and acetylation of histone H3 occur on the same histone H3 tail on nucleosomes associated with active IE gene chromatin. Chromatin immunoprecipitation (ChIP) assays were performed using antibodies that specifically recognize the doubly-modified phosphoacetylated form of histone H3. Analysis of the associated DNA shows that histone H3 on c-fos- and c-jun-associated nucleosomes becomes doubly-modified, the same H3 tails becoming both phosphorylated and acetylated, only upon gene activation. This study reveals potential complications of occlusion when using site-specific antibodies against modified histones, and shows also that phosphorylated H3 is more sensitive to trichostatin A (TSA)-induced hyperacetylation than non-phosphorylated H3. Because MAP kinase-mediated gene induction is implicated in controlling diverse biological processes, histone H3 phosphoacetylation is likely to be of widespread significance.