In recent years many studies have stressed the importance of using biological response modifiers (BRMs) in the treatment of different conditions of immune-impairment correlated with ageing, cancer and infectious diseases. In particular the use of different BRMs in conjunction with conventional therapies has been extensively explored. Our studies have demonstrated that treatment with Thymosin alpha-1 and low doses of IFN or IL-2 exert powerful biological effects both in vitro and in vivo. They are highly effective in restoring cytotoxic activities in immunosuppression induced by tumors and/or cytostatic drugs. In addition, when combined with specific chemotherapy, they are able to induce a dramatic inhibition of tumor growth in both experimental models and in humans. Immunotherapeutic treatment also has an application in controlling infectious diseases, especially those occurring in the immune-compromised host. The advantage of using the combined immunotherapy treatment with antiviral drugs has been recently demonstrated by our group both in a murine experimental influenza model and in patients infected with HBV, HCV and HIV. (C) 1997 Elsevier Science Ireland Ltd.