Rvb1 and Rvb2 are highly conserved proteins present in archaea and eukaryotes. These proteins are members of a large superfamily of ATPases associated with diverse cellular activities--the AAA(+) superfamily. The Rvbs have been found in multiprotein complexes that have wide ranges of functions, including DNA repair, transcription, chromatin remodeling, ribosomal RNA processing, and small nucleolar RNA accumulation. Here we show that yeast Rvb1 and Rvb2 form a heterohexameric ring structure rather than the double-hexameric ring structure proposed to be formed by the human proteins. The yeast Rvb1/2 complex has enhanced ATPase activity compared with the individual Rvb proteins; furthermore, the ATPase activity of the Rvb1/2 complex is further increased in the presence of double-stranded DNA with 5' or 3' overhangs. The yeast Rvb1/2 ring undergoes nucleotide-dependent conformational changes as observed by electron microscopy. In addition, consistent with a role for these proteins in chromatin remodeling and DNA repair, the yeast Rvb1/2 complex exhibits DNA helicase activity with a preference for unwinding in the 5'-to-3' direction. The individual Rvb proteins also exhibit helicase activity, albeit weaker than that of the Rvb1/2 complex. These results clearly establish the yeast Rvb1/2 complex as a heterohexameric ATP-dependent DNA helicase and highlight the possible roles played by the Rvb proteins within multiprotein complexes.