Matrix metalloproteinases (MMPs) are important enzymes in tissue turnover and various inflammatory processes. In this study, it was evaluated whether serum MMP-8 can predict the response to adjuvant interferon alfa-2b (IFN-alpha) therapy in patients with operated high-risk cutaneous melanoma. Pre-treatment sera from 460 patients with stage IIB-IIIC melanoma were analyzed for MMP-8. The patients were randomized after surgery to adjuvant IFN-alpha for 12 or 24 months (n = 313) or observation only (n = 147). The median serum MMP-8 level was used to classify the patients into a low MMP-8 (n = 232) and a high MMP-8 (n = 228) group. In the high MMP-8 subgroup, IFN-alpha therapy significantly improved relapse-free survival (RFS). RFS was 36.8 months in patients with high MMP-8 levels receiving IFN-alpha therapy, whereas RFS for those with high MMP-8 levels with observation only was 10.6 months (P = 0.027). Median overall survival for patients with high MMP-8 and observation only was 36.7 versus 71.7 months in those receiving IFN-alpha (P = 0.13). In a multivariate model, IFN-alpha therapy was a significant predictor of favorable RFS (HR 0.74; 95 % CI 0.55-0.99; P = 0.048), after adjustment for pre-treatment MMP-8 (HR 1.17; 95 % CI 0.88-1.55; P = 0.28), gender (HR 1.16; 95 % CI 0.86-1.56; P = 0.32), age (HR 1.00; 95 % CI 1.00-1.02; P = 0.12), ulceration (HR 1.09; 95 % CI 0.81-1.46; P = 0.58), and the presence of node metastases (HR 1.36; 95 % CI 1.17-1.58; P < 0.0001). In conclusion, patients with high serum MMP-8 levels may benefit from adjuvant IFN-alpha therapy, but this observation should be further investigated.