The age-related decline in dehydroepiandrosterone (DHEA) production is currently attracting attention because of its possible relevance to the etiology and management of a number of age-related clinical disorders. Various abnormalities of immune system function have been described in the elderly. Among them, increased concentrations of neopterin have been reported, which is produced by human monocytes/macrophages upon stimulation by interferon-gamma. In order to examine the relation of serum DHEA to serum neopterin, we studied 281 otherwise healthy outpatients, who visited the physician's office for a medical health check-up. 10% presented with increased neopterin concentrations, 0.4% had increased DHEA sulfate (DHEAs) concentrations. DHEAs concentrations were significantly higher in patients with lower neopterin concentrations (Mann-Whitney test: U=4793, P<0.0001). There existed a rather strong inverse correlation between DHEAs concentrations and serum neopterin concentrations (Spearman's rank correlation: r(s)=-0.221, P<0.0001). The data support the concept that the decrease of DHEA with increasing age is related to immune system activation. Oxidative stress which accompanies immune response may diminish DHEA synthesis.