Pseudomonas putida utilized methyl parathion as sole carbon and (or) phosphorus source. The bacterium elaborated the enzyme organophosphorus acid anhydrase, which hydrolyzed methyl parathion to p-nitrophenol. p-Nitrophenol was further degraded to hydroquinone and 1, 2, 4-benzenetriol. The final ring compound, 1, 2, 4-benzenetriol, was cleaved by benzenetriol oxygenase to maleyl acetate.Key words: Pseudomonas putida, organophosphorus pesticides, degradation, methyl parathion.