The extracellular polymeric substances (EPS) contained in activated sludge flocs resulting from two-sewage treatment plants were extracted according to eight methods referred to in the bibliography. Extracted EPS were characterized by their extraction yield, carbon concentration, their biochemical composition, their HPSEC chromatograms and, where possible, molecular weight (MW) distributions. With HPSEC chromatograms, the use of the mobile phase containing methanol allowed a hydrophobic mechanism for EPS, extracted partly by chemical methods, to be identified. An MW distribution (from 0.1 to 600 kDa) was established for EPS extracted by control and physical methods only, from calibration. Except for the resin and heating extraction methods, the EPS extracted from the two sludges displayed the same trend in their HPSEC fingerprints but not in their MW distribution. Results show that the extraction methods using chemical reagents strongly affected the HPSEC fingerprints of EPS, whereas, the physical methods influenced only MW distribution but not HPSEC fingerprints. The use of heat to extract EPS seems to induce hydrolysis of a part of EPS. The HPSEC fingerprint is a good indicator for the appreciation of the consequences of EPS extraction methods on the EPS extracted and the distribution of EPS with low MW in particular. (c) 2006 Elsevier B.V. All rights reserved.