Many endocrinologic disturbances have been reported during and after interferon-alpha (IFN-alpha) treatment. These disturbances have often been caused by autoantibodies. The aim of this prospective study was to evaluate whether IFN-alpha causes hormonal changes and if it is necessary to search for such disturbances routinely. Ten patients with hematologic malignancies were examined before and after 4 months of IFN-alpha treatment. Pituitary function was tested by hypothalamic releasing hormones (thyrotropin-releasing hormone, TRH, growth hormone-releasing hormone, GHRH, gonadotropin-releasing hormone, GnRH). The adrenal glands were tested with the adrenocorticotropin (ACTH) test. The human chorionic gonadotropin (hCG) test was performed on the men (n = 4). The IFN treatment was well tolerated, and no long-term hormonal side effects were found. The testosterone/sex hormone binding globulin (SHBG) index tended to improve. There were no significant differences between the hormone responses before and after IFN-alpha treatment. We conclude that the hypothalamic-pituitary axis remains intact after IFN-alpha treatment. There is no need to follow patients endocrinologically if the patients are not predisposed by autoantibodies.