Oxidative stress is implicated in the pathogenesis and complications of type 2 diabetes mellitus (NIDDM). Glycoxidation may damage the enzymes that synthesise glutathione (GSH), an endogenous intracellular antioxidant. Erythrocytes (RBCs) taken from NIDDM subjects, and non-diabetic controls, were GSH-depleted using 1-chloro-2,4-dinitrobenzene, incubated in a solution containing GSH-rebuilding substrates, and sampled for GSH using a 5,5′-γ-dithiobis-(2-nitrobenzoic acid)/enzymatic recycling procedure. NIDDM subjects, on average, had the same GSH concentration and synthesising ability as non-diabetic controls, indicating normal function of the synthesis enzymes. A positive correlation between synthesis and concentration of GSH seen in non-diabetic controls did not exist in NIDDM, due to their putatively larger oxidative load. The results, to the best of our knowledge, provide the first evidence that, despite a higher oxidative load, intact RBCs from NIDDM subjects are able to synthesise GSH normally. It is hypothesised that increased rates of GSH synthesis would maintain a normal steady-state GSH concentration.