There is some evidence that, in humans and experimental animals, psychological stress may suppress or enhance immune functions, depending on the nature of the stressor and the immune variables under consideration. The possibility that psychological stress may affect the production of pro-inflammatory and immunoregulatory cytokines was investigated in 38 medical students, who had blood samplings a few weeks before and after as well as one day before an academic examination. Psychological stress significantly increased the stimulated production of tumour necrosis factor α (TNF-α), interleukin 6 (IL-6), IL-1 receptor antagonist (IL-1Ra), interferon γ (IFN-γ) and IL-10. Students with high stress perception during the stressful condition had a significantly higher production of TNF-α, IL-6, IL-1Ra and IFN-γ than students with a low-stress perception. Students with a high anxiety response had a significantly higher production of IFN-γ and a lower production of the negative immunoregulatory cytokines, IL-10 and IL-4, than students without anxiety. These finding suggest that, in humans, changes in the production of the pro-inflammatory cytokines, TNF-α, IL-6 and IFN-γ, and negative immunoregulatory cytokines, IL-10 and IL-4, take part in the homeostatic response to psychological stress and that stress-induced anxiety is related to a T-helper-1-like response.