A large body of clinical experience on the adverse consequences of cytokine administration has accumulated since the last decade. Side-effects reported after the therapeutic use of cytokines has provided evidence that activation of the immune response may sometimes have deleterious consequences. Several effects appeared as a direct consequence of the immune activation induced by cytokines, e.g. flu-like reactions, vascular leak syndrome. Cytokine-induced exacerbation of underlying diseases or immune dysregulation were other complications of growing concern. Interferon-alpha (IFN-alpha) treatment has now been clearly linked with the exacerbation or the occurrence of several types of autoantibodies or autoimmune diseases (thyroiditis, systemic lupus erythematosus, hematologic disorders, insulin-dependent diabetes mellitus) or diseases involving altered cell-mediated immune functions (inflammatory dermatologic diseases, nephritis, pneumonitis, colitis). By contrast immunological side-effects of IFN-beta and IFN-gamma have been seldom reported. However, the extent of clinical experience with both of these cytokines is still very limited. Interleukin-2 (IL-2) has also been implicated in various conditions that may involve immunopathological processes (thyroid disorders, rheumatoid arthritis, dermatological diseases, interstitial nephritis). Growth factors have been more specifically linked with the development or the exacerbation of dermatological inflammatory diseases through neutrophils, monocytes/macrophages or eosinophils activation (e.g. cutaneous vasculitis and generalized cutaneous eruption, Sweet's syndrome, bullous eruption, psoriasis). Exacerbation of autoimmune thyroiditis was described with granulocyte-macrophage colony-stimulating factor (GM-CSF) only. The immunogenicity of cytokines is also of great relevance and the occurrence of antibodies binding IFN-alpha and IFN-beta, IL2 and GM-CSF have been reported. While the clinical significance of non-neutralizing antibodies is not clearly established, an absence of response or reversal of clinical efficacy has been described in patients developing neutralizing antibodies. Finally, several isolated reports have recently suggested that IFN-alpha treatment may be associated with several immunosuppressive effects while IL-2 is clinically associated with an increased incidence of infectious complications.