The Pseudomonas spp. from a commercial bioaugmentation product were characterized so that they might be monitored in a waste treatment system. The product CX 80 was chosen because of its use in the biodégradation of aromatic compounds. Four Pseudomonas spp. were selected - three P. putidaspp., IGA 7.16, IGA 7.24 and IGA 0.92, and one P . fluorescenssp., IGA 13.42. The organisms were morphologically identical and were not readily distinguishable using biochemical tests. They had similar growth properties when grown on benzoate, naphthalene, phenol and m-toluate. IGA 7.16 alone was capable of growth on toluene and p-chlorophenol. A large plasmid band (85-120kb) was detected in IGA 7,16, IGA 7.24 and IGA 0.92. Southern hybridization to a 32P-labelled probe and dot blot hybridization to a non-radioactively labelled probe confirmed the presence of a NAH plasmid in IGA 7.24 and a TOL plasmid in IGA 7.16. P.putida IGA 7.24 was added to an activated sludge system in order to note the effect of bioaugmentation and to monitor the survival of the organism in the system. The response of the activated sludge to naphthalene with and without the addition of IGA 7.24 was similar. The systems adapted rapidly to naphthalene. Colony hybridization using a nonradioactively labelled NAH probe was more sensitive than vapour plates in the early detection of the emerging naphthalene degrading population.