Acid orange 52 (AO52), extensively used in textile industries, was decolorized by Pseudomonas putida mt-2. AO52 azoreduction products such as N,N'-dimethyl-p-phenylenediamine (DMPD) and 4-aminobenzenesulfonic acid (4-ABS), were identified in the static degradation mixture. These amines were identified only in media of static incubation, which is consistent with their biotransformation under shaken incubation (aerobic conditions). Tests with azo products were carried out, and whole cells were found able to easily degrade DMPD contrary to 4-ABS. However, this last could be attacked by cell extract, and an oxygen uptake was observed during the reaction. Degradation of DMPD by entire cells led to the formation of catechol. These results show that P. putida was able to decolorize AO52 and metabolize its derivative amines. In addition, the ability of tested compounds was evaluated in vitro to reduce human plasma butyrylcholinesterase (BuChE) activity. Azoreduction products seem to be responsible for BuChE inhibition activity observed in static biodegradation extract. However, toxicity of AO52 completely disappears after shaken incubation with P. putida, suggesting that bacterium has a catabolism which enables it to completely degrade AO52 and especially, to detoxify the dye mixture.