Studies of bacterial regrowth in drinking water distribution systems have clearly shown the importance of biofilms attached to the inner surface of pipes. These microorganisms represent potential sources of contamination and provide habitats for opportunistic pathogenic microorganisms. To understand the bacteriological phenomena that occur in distribution systems, it is important to quantify the attached biomass. This paper describes different analytical methods developed to quantify biofilms in drinking water distribution systems. The methods include: total organic carbon measurement; polysaccharide measurement; DNA quantification; protein measurement; use of an INT Redox probe; and, measurement of potential exoproteolytic activity.