INTRODUCTION: With the proliferation of researchers investigating various aspects of RNA biology has come a corresponding proliferation of commercially available kits for RNA purification. Some of these kits have specialized uses and applications, and it is not always possible to simply mix and match the different protocols. Although the instructions are often written with a minimum of specifics concerning the chemical basis for the separation characteristics that the kits use, the competent researcher will want to understand these important features. Unfortunately, commercial sources work hard to hide the specifics of their methods. Fortunately, patent documents are publicly available, and the government mandates material safety data disclosures of the composition of at least those components that represent a threat to environmental health and safety. Thus, it is possible to infer many aspects of such "proprietary" materials, which in most cases are only slightly and unimportantly modified from published techniques. We do not describe in detail the specific steps involved in the use of particular kits; they are detailed in the literature that comes with each kit and their components (e.g., proprietary buffers). Instead, we detail some advantages and disadvantages of using RNA purification kits.