Bacterial contamination may cause several adverse reactions, including pyrogenic consequences during hemodialysis. Some disorders, such as skin flush, pruritus, and other anaphylactoid reactions, are still unexplained. Bacterial bioproducts, i.e., endotoxins, are not removed by the highly porous membranes. Most studies have been done on the liquid phase of the dialysate. In this study, a biofilm has been made in a hemodialysis system, using an additional pump that continuously supplies several bioproducts: gram (+) or gram (-) bacteria, or extracted endotoxin. The attachment of bacteria and the role of the biofilm in different circumstances were determined: 1) A contaminated dialysate with 1,000 bacteria/ml is necessary to set up a biofilm in the device. AAMI, Canadian, and French standards (200 bacteria/ml) are validated. 2) In the presence of non-endotoxic bacteria (Staphylococcus conhii, delta hemolytic), and when solutions contaminated by endotoxin are used, the biofilm produces micellar forms of endotoxin that are not removed by the filter. 3) The efficiency of disinfectants differs. For example, the activities of sodium hypochlorite, formaldehyde, and hydrogen peroxide are lower in the biofilm than in static studies.