The aim of this study was to evaluate the effect of oral supplementation with two different cysteine-rich whey protein formulas on plasma GSH levels and parameters of oxidative stress and immune status in HIV-infected patients. Plasma concentrations of TNF-alpha and interleukins 2 and 12 (P > 0.08, all comparisons) as well as routine clinical parameters remained unchanged. Therapy was well tolerated. In glutathione-deficient patients with advanced HIV-infection, short-term oral supplementation with whey proteins increases plasma glutathione levels. A long-term clinical trial is warranted to see if this "biochemical efficacy" of whey proteins translates into a more favorable course of the disease.