Pseudomonas putida CPI grew on all three mono-chlorophenol isomers when supplied as the sole source of carbon and energy. The biodegradability of the mono-chlorophenols followed the order: 4-chlorophenol > 2-chlorophenol > 3-chlorophenol. P. putida CPI was able to degrade 300 ppm 4-chlorophenol, 250 ppm 2-chlorophenol and 200 ppm of 3-chlorophenol. In the presence of fructose (1%, w/v) the organism could degrade 400 ppm 4-chlorophenol, 500 ppm 2-chlorophenol and 300 ppm 3-chlorophenol. Chlorophenol removal was stimulated in the presence of low concentrations of glucose (0.05% - 0.5%, w/v). Substrate removal was inhibited and there was a significant fall in pH with concentrations of glucose greater than 1.0% (w/v). When the pH was controlled at pH 7.0 inhibition of substrate removal was alleviated. The rate of removal of mono-chlorophenols was greater in the presence of fructose than in the presence of glucose, yeast extract or a combination of fructose and yeast extract. P. putida CPI formed clumps of cells when grown on all three monochlorophenol isomers and fructose but not when grown on glucose, yeast extract or phenol. When the organism was grown on a combination of chlorophenols and an additional carbon source clumping was present but to a lesser degree. Monitoring growth of the organism by a direct microscopic count technique was found to be more representative than other methods including optical density measurements, dry weight measurements and the plate count technique. A change in shape of the bacterium from rod shape to a coccus shape coupled with a reduction in cell size was noted when the organism was grown under nutritional stress. Isomerization of cis to trans forms of the unsaturated fatty acids in P. putida CP1 occurred under conditions of environmental stress. Trace amounts of the polyunsaturated fatty acid linoleic acid (cis-9, cis-12- octadecadienoic acid) rarely found in bacterial membranes, was detected in the membrane of P. putida CP1.