The tripeptide glutathione (L-gamma glutamyl-L-cysteinyl glycine) (GSH) is the most abundant antioxidant inside cells. Intravenous administration of GSH decreases both the peroxidative stress of patients with septic shock and the toxicity of cytotoxic drugs. Since glutamine is a precursor of GSH, supplementation in TPN could be used to maintain high blood and tissue levels of GSH and thus minimise toxicity and oxidative stress damage. We are currently investigating stability of an intravenous GSH preparation in TPN admixtures and the likely GSH circadian rhythm variations in volunteers and patients (poster presentations at BAPEN 2000).