Two important commercial surfactants, linear alkylbenzene sulphonate (LAS) and alcohol ethoxylate (AE), were tested for their biodegradation in confirmatory continuous activated sludge (CAS) systems, according to the simulation OECD 303A method. Two commercial LAS products, produced from two C 10 -C 13 alkyl chain LABs of our production, the first using HF and the other AlCl 3 as catalyst, and one commercial AE derivative, obtained from C 12 -C 15 alkyl chain oxoalcohol of our production and with an average ethoxylation degree of 7 were examined. The innovative aspect of such a biodegradation study consists in the application of specific analytical methodologies, using high performance liquid chromatography (HPLC) as final detection technique, to determine the residual amount of the surfactants (in case of LAS also of the biodegradation intermediates) in effluents and sludges of the CAS tests in addition to DOC (Dissolved Organic Carbon) measurements. This allows to get a specific assessment of the degree of the primary and ultimate biodegradation of LAS which can be attained when it is disposed in sewage treatment plants. The results obtained by HPLC for the primary biodegradation are > 99% for the three studied species. The ultimate biodegradation rates determined by HPLC are with 95 % (LAS-HF) and 98% (LAS-AlCl 3 ) more than 10% higher than those obtained via DOC determination (84.9 and 85.1 %, resp.).