Systemic administration of human interferon-alpha stimulates the pituitary-adrenal axis in men, but the exact mechanism still remains to be established. The present study was undertaken to examine the hypothesis that interferon-alpha may alter the circulating concentrations of the cytokines which involve the activation of the pituitary-adrenal axis. Eleven patients with chronically active hepatitis C were treated with human lymphoblastoid interferon-alpha (IFN: 6 x 10(6) IU/day) and changes in plasma adrenocorticotropin (ACTH), serum cortisol and cytokine concentrations were observed on both the first and second days of the treatment. Subcutaneous administration of IFN significantly increased plasma ACTH and serum cortisol concentrations by 3 h after the injection. Serum interleukin-6 (IL-6) increased with the increase in circulating ACTH and cortisol. There was a significant correlation between serum cortisol and IL-6 concentrations at 3 h. In contrast, an increase in serum interleukin-1 beta was only observed in one case. On the second day of IFN treatment, simultaneous administration of 25 mg diclofenac sodium eliminated the IFN effects on circulating ACTH, cortisol and IL-6 concentrations. The present studies demonstrated that circulating IL-6 increases after systemic IFN administration, resulting in activation of the pituitary-adrenal axis.