Organophosphate (OP) pesticides are used worldwide in agriculture, producing a market of around 30 billion dollars per year. Although OPs are highly toxic for humans, many bacteria are not affected by their presence, and some bacterial enzymes are able to hydrolyse OPs into non-toxic compounds. Of particular interest is the recent emergence of a number of phosphotriesterases (PTEs), especially in some bacteria found in soil, such as Agrobacterium radiobacter and Pseudomonas diminuta. These enzymes are binuclear metallohydrolases and are able to degrade a wide range of phosphotriesters, including various pesticides and nerve gas agents (e.g. sarin). Thus they have received attention for their potential use in detoxification of contaminated soil and water. Recently, a series of highly efficient b-lactamase-related methyl parathion hydrolases (MPHs) have been isolated from several bacterial strains. In addition, a glycerophosphodiesterase (GpdQ) discovered from Enterobacter aerogenes with activity towards stable aliphatic phosphodiesters as well as promiscuous activity towards phosphotriesters and phosphomonoesters has been characterised recently. These enzymes join the ranks of OP-degrading enzymes as potential bioremediation agents. Here, we will review the properties, functions and structures of these binuclear metallo-hydrolases, with focus on the well-characterised PTEs.