Human Elongator complex was purified to virtual homogeneity from HeLa cell extracts. The purified factor can exist in two forms: a six-subunit complex, holo-Elongator, which has histone acetyltransferase (HAT) activity directed against histone H3 and H4, and a 3-subunit core form which does not have HAT activity in spite of containing the catalytic Elp3 subunit. Elongator is a component of early elongation complexes formed in HeLa nuclear extracts, and can interact directly with RNA polymerase II in solution. Several human homologues of the yeast Elongator subunits were identified as subunits of the human Elongator complex, including Stat Interacting Protein 1 (StIP1), and IKK-complex-Associated Protein (IKAP). Mutations in IKAP can result in the severe human disorder familial dysautonomia, raising the possibility that this disease might be due to compromised Elongator function and therefore could be a transcription disorder.