Oxygen-sensing chemoreceptors contribute significantly to the regulation of the respiratory drive and arterial PO(2) levels. The hypoxic ventilatory response (HVR) decreases strongly with age and is modulated by prolonged hypoxia and physical exercise. Several earlier studies indicated that the regulation of the ventilatory response and erythropoietin (EPO) production by the respective oxygen sensors involves redox-sensitive signaling pathways, which are triggered by the O(2)-dependent production of reactive oxygen species. The hypothesis that HVR and EPO production are modulated by thiol compounds or changes in the plasma thiol-disulfide redox state (REDST) was investigated. It was demonstrated that both responses are enhanced by oral treatment with N-acetyl-cysteine (NAC) and that HVR is correlated with plasma thiol level and REDST. Results suggest the possibility that age-related changes in plasma REDST may account for the age-related changes in HVR.