Hydro1uinone (HQ) was administered in degassed distilled water to groups of 10 male and 10 female rats at dose levels of 0, 20, 64, or 200 mg/kg/day by gavage, five days/week for 13 weeks. A functional-observational battery (FOB) was used to detect functional impairment of the nervous system three days prior to exposure to HQ and at 1, 6, and 24 hr and 7, 14, 30, 60, and 91 days after administration of the initial dose. At the end of the exposure period, six males and six females were fixed by intravascular perfusion and central nervous system (CMS) and peripheral nervous system (PNS) tissues were examined after staining with hemotoxylin and eosin or Luxol Fast Blue and Bodian silver impregnation techniques. The PNS was also examined following plastic embedment and toluidine blue staining of sciatic and tibial nerve tissues. All 10 male and 10 female rats were necropsied and abdominal and thoracic organs were examined for macroscopic lesions and brain and kidney weights were measured.