IFN-alpha administration after primary tumour resection improves the survival of melanoma patients at high risk of relapse. To investigate whether this response might be due to stimulation of anti-tumour immunity, the effect of IFN-alpha on anti-melanoma CTL generation in MLTC was measured. IFN-alpha increased both allogeneic and autologous anti-melanoma CTL generation from peripheral blood lymphocytes stimulated with irradiated primary melanoma cultures. IFN-alpha up-regulated MHC class I expression on primary melanoma cultures, whereas IFN-gamma up-regulated both MHC class I and II expression. However, the effect of IFN-alpha on anti-melanoma CTL generation was often more potent than that of IFN-gamma, equalling the effect of the optimal combination of IL-2 and IL-12. Pre-treatment of primary melanoma cultures with IFN-gamma was sufficient for CTL generation in MLTC, whereas IFN-alpha needed to be present during the MLTC. While direct anti-proliferative effects of IFN-alpha on some tumour cells have been described, IFN-alpha did not inhibit proliferation of primary melanoma cultures. These results suggest that the clinical effects of IFN-alpha in melanoma patients may be immune-mediated.