The group of chemicals designated organophosphorus compounds have had a significant impact on modern life, including use as pesticides, industrial plasticizers and chemical warfare agents. Exposure to certain organophosphates produces a delayed degeneration of the longest and largest nerve fibers, including those of the ascending and descending tracts of the spinal cord, a condition termed organophosphorus ester-induced delayed neuropathy (OPIDN). Recorded incidents of such an effect in humans have led to research regarding this neurological disease. Among the OPIDN-inducing agents is mipafox, an organophosphate insecticide, the compound we chose to employ in our studies. Although the hen is the primary experimental model in the safety assessment of organophosphates, current research has suggested that the rat may have some validity as an experimental model. We examined the sequential neuropathic effects of a single dose of mipafox (30mg/kg) in rats and hens on a comparative basis to determine the better experimental model. / Master of Science