Effects of chemical exposure on GSH redox in humans. We have performed 2 clinical studies which indicate that chemical exposure alters sulfur amino acid homeostasis as detected by changes in plasma GSH and Cys pools. As indicated above, one of these showed that GSH redox became more oxidized as a consequence of chemotherapy (33). A second study showed that both Cys and GSH pools were oxidized in individuals who smoked cigarettes compared to those who do not (34, 38). Together, these studies indicate that chemical exposures can induce significant changes in Cys and GSH homeostasis.