GSH plays vital roles in antioxidant defense mechanisms and in other physiological functions. Evidence implicating oxidative stresses in diseases prevalent in premature infants indicates that the GSH status of these infants may represent a functional deficit. GSH synthesis begins with the rate-limiting, ATP-dependent addition of cysteine to glutamate by GGCS, which exists as a dimer of non-identical subunits. The heavy chain subunit contains the active site and the light subunit is important in control of enzyme activity. To determine whether enhanced GSH synthetic capacity would augment antioxidant defense functions, we used liposome-mediated transfer of the cDNAs for rat GGCS heavy or light subunit to transfect Chinese hamster ovary (CHO) cells. CHO cell GGCS activities have been increased from 0.50±0.09(mean±SD) mU/mg protein to 10.63±2.96 by transfection with the heavy chain subunit and to 0.96±0.12 with the light chain subunit(n=4-6). CHO cell lines with stably enhanced GGCS activities also have been developed by transfection with vectors containing the GGCS heavy subunit and hygromycin/neomycin resistance genes. Northern analysis of the CHO cells that showed increased GGCS activities indicate increased transcription of the transfected GGCS gene. Studies of the relative sensitivities to selected toxicants of these altered cell lines will be useful in assessing the potential for increasing cellular resistance to metabolic stresses through similar enhancement of GSH synthetic capacity. (We gratefully acknowledge support from the Wyeth Pediatrics Neonatology Research Grants Program and HD27823).