Tests of the biodegradation of the azo dyes Reactive Black 5 and Reactive Yellow 145 confirmed the low biodegradability of these components in the considered conditions, namely a strain of Pseudomonas fluorescens, cultivated at 25 degrees C, an initial pH of 7 and in presence of a supplementary carbon source, glucose. Indeed, for an initial dye concentration of 40 ppm, the maximum yields of decolouration were 27% and 18% for the two dyes RB5 and RY145. Some tests of biological mineralisation of solutions preliminary photocatalysed demonstrate a mineralisation of the considered solutions for various irradiation times. Identification of the intermediate by-products is in progress to propose a reaction pathway.