Nephrologists are presented with a range of choices when selecting a dialyzer for chronic hemodialysis. Dialyzers differ in the material, structure, permeability and surface area of their membrane, and how the dialyzer is sterilized. Opinions vary regarding the impact of dialyzer characteristics on patient outcomes and which, if any, of these properties to take into account when choosing a dialyzer can be confusing. In the general dialysis population, there is no compelling evidence that the choice of a membrane material from among those materials currently in clinical use has a significant impact on morbidity or mortality (although there are rare patients who will react adversely to a given dialysis membrane). Similarly, most dialyzers are capable of adequately removing small solutes, such as urea, provided they are used with an appropriate blood flow rate and treatment time to ensure delivery of a single-pool Kt/Vurea of at least 1.25 for men and 1.65 for women. However, in some dialysis patient subpopulations, the results of randomized clinical trials suggest that use of dialyzer containing high-flux membranes confers an outcome advantage. The extent to which this advantage is realized might also depend on how the dialyzer is used, with application in convective therapies such as hemodiafiltration being superior to diffusive therapies such as hemodialysis. This possibility is currently the subject of several large clinical trials.