A mixed bacterial culture, consisting of a minimum of nine isolates, was adapted to growth on technical parathion (PAR) as a sole carbon and energy source. The primary oxidative pathway for PAR metabolism involved an initial hydrolysis to yield diethylthiophosphoric acid and p-nitrophenol. A secondary oxidative pathway involved the oxidation of PAR to paraoxon and then hydrolysis to yield p-nitrophenol and diethylphosphoric acid. Under low oxgen conditions PAR was reduced via a third pathway to p-aminoparathion and subsequently hydrolyzed to p-aminophenol and diethylthiophosphoric acid. PAR hydrolase, an enzyme produced by an isolate from the mixed culture, rapidly hydrolyzed PAR and paraoxon (6.0 mumol/mg per min). This enzyme was inducible and stable at room temperature and retained 100% of its activity when heated for 55 C for 10 min.