An enzyme in E. coli that hydrolyzes diisopropylphosphorofluoridate (DFP) has now been found to hydrolyze the nerve gas 1,2,2- trimethylpropylmethylphosphonofluoridate (soman) many times faster. With either substrate the E. coli enzyme is stimulated manyfold by 10(-3) M Mn2+. These criteria are combined and applied to this, and to a superficially similar but distinctly different, enzyme found in squid nerve. The results suggest that while several tissues of the squid contain only this second kind of DFP hydrolyzing enzyme, termed squid type DFPase , many other sources including E. coli contain a mixture of squid type DFPase (the name not strictly indicative of source) and the other DFP hydrolyzing enzyme, now termed Mazur type DFPase . Procedures for the purification of Mazur type DFPase from hog kidney, while increasing the specific activity for DFP hydrolysis may actually have been enriching the purified material in the squid type DFPase . Because E. coli has the highest soman hydrolyzing capacity of any source so far examined, this organism is a promising source for the development of new purification procedures for Mazur type DFPase .