A complex of two TFIID TATA hox-binding protein-associated factors (TAF(II)s) is described at 2.0 Angstrom resolution. The amino-terminal portions of dTAF(II)42 and dTAF(II)62 from Drosophila adopt the canonical histone fold, consisting of two short alpha-helices flanking a long central alpha-helix. Like histones H3 and H4, dTAF(II)42 and dTAF(II)62 form an intimate heterodimer by extensive hydrophobic contacts between the paired molecules. In solution and in the crystalline state, the dTAF(II)42/dTAF(II)62 complex exists as a heterotetramer, resembling the (H3/H4), heterotetrameric core of the histone octamer, suggesting that TFIID contains a histone octamer-like substructure.