Since its introduction in the United States more than two decades ago, the practice of dialyzer reuse has continued to grow. In recent years, it appears to have been based mainly on economic, rather than medical, considerations. However, adverse reactions, such as immune hemolytic anemia caused by anti-Nform antibody associated with dialyzer reuse, and infectious outbreaks have been reported. The validity of earlier reports suggesting improved morbidity and mortality in patients dialyzed with reprocessed dialyzers have been disputed with recent data. In the current Dialysis Morbidity and Mortality Study (DMMS), we collected demographic, comorbidity, laboratory, treatment, socioeconomic, and insurance data on a large random sample of approximately 20,000 of the US dialysis patient population over a 3-year period, using the dialysis records. Data were collected predominantly on patients receiving incenter hemodialysis as of December 31, 1993. Morbid and mortal events through 1996 were examined in relation to various patient and dialysis unit characteristics. The results show that there has been a significant increase in the practice of dialyzer reuse in the United States. Large regional differences exist, and reuse is greatest in freestanding for-profit (FSFP) units (87%) and freestanding nonprofit (FSNP) units (77%) and least in hospital units (49%). There has been a significant increase in the proportion of units using Renalin (Minntech, Minneapolis, MN) and a substantial decrease in the proportion of the units using formalin. Approximately 15% of the units each year switch the type of sterilant.