We report the in vitro selection of deoxyribozymes that catalyze the Diels-Alder reaction between anthracene and maleimide substrates. Previous work showed that ribozymes can catalyze this reaction with substantial rate enhancement. We viewed the direct comparison of DNA and RNA enzymes as an opportunity to test the relative catalytic efficiencies of DNA and RNA. Many new deoxyribozymes were identified; one of these, DAB22, can catalyze the in trans reaction of untethered anthracene and maleimide substrates with rate constant and rate enhancement values comparable to those of the analogous ribozyme (e.g., k(obs), 3 min(-1) and rate enhancement > 4 x 10(5) for the deoxyribozyme). These findings provide evidence that DNA enzymes can catalyze carbon-carbon bond formation as efficiently as the best known RNA enzymes, despite the absence of 2'-hydroxyl groups in DNA.