Xylene isomers and mixed xylenes were administered to male and female Sprague-Dawley rats to evaluate their effects on standard toxicological parameters which included body and organ weights, hematology, serum chemistries, urinalysis and histopathological examination. In the initial study, m, o- or p-xylene were administered in corn oil by gavage for 10 consecutive days at dose levels of 250, 1000 and 2000 mg/kg/day. The most noteworthy changes were increased liver weight in both sexes for all three isomers while decreases in spleen and thymus weights were seen less frequently. Rats were subsequently exposed to mixed xylenes by gavage in corn oil for 90 consecutive days at dose levels of 150, 750 and 1500 mg/kg/day. The most significant findings of the subchronic study were enlarged livers and kidneys. Histopathological evaluation of liver and kidney tissues revealed an increased incidence of minimal chronic renal disease in only female rats, while treatment related hepatic histopathological changes were not detected in either sex.