This protocol describes the analysis of human hepatocarcinoma cells (Hep G2) for reduced and oxidized glutathione, following treatment with nanoparticle formulations, as part of the NCL in vitro preclinical characterization cascade. A shift from reduced to oxidized glutathione is indicative of oxidative stress, while a decrease in the overall reduced glutathione pool is indicative of conjugative metabolism or impaired synthesis (1). This protocol utilizes a colorimetric method for glutathione determination.