Here we report that supplementation of a common compound betaine (1-carboxy-N,N,N-trimethylmethanaminium inner salt) enhances restriction digestion of DNA molecules being resistant to digestion despite the existence of recognition sites. A previous study reported total isostabilization of DNA was achieved in the presence of 5.2 M of betaine, however, we have observed the enhancement of restriction kinetics at 0.3 M of betaine, therefore, it likely provided some catalytic proficiency to restriction enzymes rather than the induction of DNA conformational changes. Betaine also enhances catalytic efficiency of PCR, and our result of restriction digestion, taken together, suggests potential application of betaine in other enzymatic reactions in an aqueous solution. (c) 2005 Elsevier Inc. All rights reserved.