Details regarding dialysis therapy have been studied by the US Renal Data System (USRDS) in four random samples of US hemodialysis patients during the years 1986 to 1997. During this decade, the delivered dose of hemodialysis therapy has increased by at least 0.2 Kt/V. The frequency of twice weekly dialysis prescription decreased, whereas the duration of each treatment showed only minor changes. A large shift to more biocompatible membranes, particularly to synthetic membranes, was observed. The use of acetate dialysate almost disappeared. Outcomes research by the USRDS showed significantly lower mortality risk associated independently with higher delivered Kt/V, substituted cellulose or synthetic membranes, and bicarbonate dialysate. The projected reduction in mortality risk from these changes in hemodialysis therapy was of a similar magnitude to the observed 14% to 17% reduction in mortality rate during the years 1990 to 1996. National observational studies of dialysis patients may influence the practice of dialysis and lead to improved survival.