We used Glucose 6 phosphate dehydrogenase (G6PD) minus cells (89 cells) and G6PD containing cells (KI) to understand the mechanisms of bioreduction of disulfide and the redox regulation of protein and non protein thiols in mammalian cells. The 89 cells reduce hydroxyethyldisulfide (HEDS) to mercaptoethanol (ME) at a slower rate than K1 cells. HEDS reduction results in loss of nonprotein thiols (NPSH) and a decrease in protein thiols (PSH) in 89 cells. The effects are less dramatic with K1 cells, However, the loss of NPSH and PSH in K1 cells are increased in the absence of glucose. Glutathione-depletion with L-BSO partially blocks HEDS reduction in K1 and 89 cells. Treatment with the vicinal thiol reagent phenyl arsenic oxide (PAO) blocks reduction of HEDS in both cells. Surprisingly, dehydroepiandrosterone (DHEA), a known inhibitor of G6PD, inhibits the growth and blocks the reduction of HEDS both in 89 and K1 cells suggesting that its mechanism for inhibition of growth is not G6PD related.