The RNase-Free DNase Set provides efficient on-column digestion of DNA during RNA purification using RNeasy Kits or the QIAamp RNA Blood Mini Kit. Generally, DNase digestion is not required for RNA purified with RNeasy Kits since the silica-gel–membrane, spin-column technology efficiently removes the majority of the DNA without DNase treatment. However, more complete DNA removal using the RNase-Free DNase Set may be necessary for certain RNA applications that are sensitive to very small amounts of DNA. Buffer RDD, included in the set, is optimized for on-column DNase digestion for 15 minutes at 20–30°C. The buffer is also well-suited for efficient DNase digestion in solution. For DNase treatment when using the RNeasy 96 Kit, please contact QIAGEN Technical Services or your local distributor for a separate, optimized protocol. One Kunitz unit is defined as the amount of DNase I that causes an increase in A260 of 0.001 per minute per milliliter at 25°C, pH 5.0, with highly polymerized DNA as the substrate (Kunitz, M.  Crystalline desoxyribonuclease. I. Isolation and general properties, spectrophotometric method for the measurement of desoxyribonuclease activity. II. Digestion of thymus nucleic acid (desoxyribonucleic acid): the kinetics of the reaction. J. Gen. Physiol. 33, 349 and 363).