A commercial mixed culture, Biolyte HAB, degraded mono-chlorophenols using a metci- cleavage pathway. 2- and 3-chlorophenol degradation was incomplete, leading to the accumulation of dead-end metabolites. Biolyte HAB was capable of the complete degradation of 2.34 mM 4-chlorophenol, via the intermediate 5-chloro-2- hydroxymuconic semialdehyde, using the meta- cleavage pathway. Pseudomonas putida CPI degraded mono-chlorophenols to completion via an orthocleavage pathway. The ability of P. putida CPI to degrade mono-chlorophenols was in the order o f 4-chlorophenol > 2-chlorophenol > 3-chlorophenol. 2- and 3-chlorophenol were degraded at concentrations o f 1.56 mM, while 4-chlorophenol was degraded at concentrations of 2.34 mM. Growth of P. putida CPI on the mono-chlorophenols resulted in the formation of large clumps of cells in the culture medium. When P. putida CPI was added to Biolyte HAB, biodégradation of monochlorophenols was significantly enhanced. Degradation occurred via the orthocleavage pathway. Although the mixture displayed similar degradative abilities to P. putida CPI, higher concentrations of chlorophenol were degraded and at increased rates. Addition of increasing concentrations of Biolyte HAB to P. putida CPI resulted in increased rates of chlorophenol degradation. Times of degradation and lag periods decreased proportionately with increasing Biolyte HAB inocula sizes. The beneficial effect of Biolyte HAB on the degradation of mono-chlorophenols by P. putida CPI was greatest for 3-chlorophenol, followed by 2-chlorophenol and finally 4- chlorophenol. Generation of a rifampicin mutant of P. putida CPI allowed for its survival in the mixed culture to be studied. P. putida CPI was capable of surviving following its addition to the mixed culture. Total bacterial numbers, chlorophenol degrading numbers and P. putida CPI numbers were found to increase with substrate removal. Increases in P. putida CPI numbers were greater with increasing concentrations of Biolyte HAB.