Previous trials with various treatments have not shown satisfactory therapeutic results for cutaneous metastasis of malignant melanoma (MM). We report three patients who were treated with peritumoral injection of interferon (IFN)-beta for multiple skin metastases of MM. The metastatic tumours were infiltrated by significant numbers of CD8+ TIA+ cytotoxic lymphocytes, and the numbers of CD4+ cells and human leucocyte antigen-DR+ cells increased after IFN-beta injection. These results suggest that the peritumoral administration of IFN-beta enhanced the antitumour immune response against the MM, suggesting that it is a promising supportive treatment for skin metastasis of MM.