Marked hyperglycaemia (30.9 mmol l(-1)) during interferon-gamma (IFN-gamma) therapy for asymptomatic recurrent renal cancer as multiple lung metastases in a 52-year-old man is described. Although the involvement of IFN-gamma has been reported in the development of autoimmune diabetes, in this case, antibodies against pancreatic beta-cells including anti-islet cell antibody (ICA) and anti-glutamic acid decarboxylase (GAD) antibody were negative. Moreover, serum level of immunoreactive insulin (IRI) (11 microU ml(-1) at fasting) and urinary excretion of C-peptide (108 microg day(-1), reference range: 20-130) suggested insulin resistance, supported by results of insulin tolerance tests. With insulin therapy and cessation of IFN-gamma, fasting blood glucose concentration returned to 6.2 mmol l(-1), and insulin therapy was discontinued. The injection of IFN-gamma may cause hyperglycaemia because of insulin resistance, rather than beta-cell injury.