Results of phenol biodegradation by both, free and immobilized Pseudomonas putida cells are presented. The influence of pH and the initial substrate concentration was analyzed. On the other hand, several tests of cell adaptation were carried out in order to increase the capacity and the rate of the biodegradation. The behaviour of free and immobilized microorganisms, was similar, reaching a maximum biodegradation capacity of 2000 ppm at an initial pH 6.6 and temperature 30 degrees C. Finally, two different kinetic models, for low and high phenol concentration were assayed.