OBJECTIVE: Proinflammatory cytokines have the potential to activate the hypothalamo-pituitary-adrenocortical (HPA) axis, and HPA axis hyperactivity is also encountered in depression. Therefore, the induction of depressive symptoms by interferon-alpha (IFN-alpha) may be mediated by changes in the cytokine network and the HPA axis. METHODS: In 17 hepatitis C patients undergoing IFN-alpha treatment, depressive symptoms were measured using the Montgomery-Asberg Depression Rating Scale (MADRS). In addition, serum cytokine concentrations were measured. Saliva was collected five times over the course of a day in order to assess daily average cortisol (DAC) and awakening response. Assessments were carried out at baseline and six later time points after starting treatment. RESULTS: During treatment, the increases in the MADRS were significantly and positively correlated with soluble interleukin (IL)-2 receptor, tumor necrosis factor alpha (TNF-alpha), and IL-6. There were no significant associations between the DAC or cortisol awakening response with the MADRS score. CONCLUSION: Results suggest a clear connection between IFN-alpha-induced depressive symptoms and cytokine concentrations, but not cortisol.