The paper describes six years of research designed to validate the use of the rat as a viable alternative to the hen for screening and mechanistic studies of neuropathic OP compounds. To date the results indicate that if morphological rather than behavioral endpoints are used, the rat may be a more valid indicator of OPIDN. The authors must, however, test the rat with a wider variety of test OPs to substantiate further the NTE/pathology relationship. Over and above the regulatory considerations, the rat, can be successfully used to address, the mechanistic questions of OPIDN and will hopefully be used to unravel those events occurring between OP exposure and the onset of pathological damage.