Abstract 1. 1. Supernatant solutions from kidney and liver homogenates of the chicken. Gallus domesticus, were found to hydrolyze the organophosphate (OP) compound diisopropylfluorophosphate (DFP). The activity on DFP as substrate was heat-inactivated and was characterized for temperature and pH optima, enzyme kinetics, and requirements for manganous ion. 2. 2. Gel column chromatography indicated that the DFPase in both tissues is in the range of 82,100 to 93,300 D. This activity is strongly inhibited by N,N'-diisopropylphosphorodia-midofluoridate (mipafox). 3. 3. The chicken has organophosphate acid (OPA) anhydrase activity comparable to other eucaryotic sources in its ability to hydrolyze DFP. Although birds may not have paraoxonase activity comparable to mammalian species, they do not differ significantly in the ability to hydrolyze DFP and probably related compounds.