Over the past few years it has better been realized how individual the needs for the effectiveness ("dose") of dialytic therapy are and which treatment related factors affect the morbidity and mortality of dialysis patients. Although the role of urea, a marker of small molecular weight uremic toxins, has been challenged, most studies have been based on kinetics of urea during and between dialyses. The dose of dialysis affects also the nutritional status and a special role for "middle" molecules as anorectic factors has been suggested. This article gives an in-depth view of some factors which affect the needs for the effectiveness of dialytic therapy, a summary of the goals of the treatment, and some practical guidelines how to reach them.