The degradation of phenol and the mono-chlorophenol isomers by a bioaugmentation product was investigated. The product comprised a mixed microbial culture which included several bacterial species, including Pseudomonads, and a brown rot fungus. Concentrations of phenol, up to lSOOmgl"1, were metabolised by the mixed microbial culture. Complete removal of 4-chlorophenol, when present as the sole carbon source, was achieved at concentrations up to 200mgl'1. Removal of both 3- and 2- chlorophenol was relatively poor, as a result of an unproductive meta-cleavage pathway. Additional carbon, detected in the product formulation, was found to inhibit removal. Phenolic removal was inhibited in the presence of increasing concentrations of glucose, but not fructose. Acclimation was found to influence the rate of removal of the additional carbon and therefore the response of the cells to this carbon. The cells had been previously exposed to glucose in the product formulation and its removal was rapid. In contrast, no acclimation to fructose had taken place and preferential removal of the phenolic from the phenolic/fructose mixtures was observed. Following acclimation of the cells to fructose, which altered the rate of utilisation of the sugar, fructose exerted inhibitory effects on phenolic removal. Inhibition due to the presence of additional carbon was found to be alleviated by incubation at lower temperatures, due to changes in substrate removal patterns. A continuous presence of the sugar, under controlled pH conditions, also facilitated complete phenolic removal. Environmental conditions, particularly temperature and acclimation, were therefore considered fundamental to the successful performance of this mixed microbial culture. Bacterial species capable of growth on 4-chlorophenol were isolated from the product. Bacteria capable of growth on 3- or 2-chlorophenol could not be isolated in pure culture. The fungus, when grown in pure culture, could not grow on 3-chlorophenol. It was capable of growth on 2-chlorophenol, but did not perform successfully as a member of the mixed culture.