Melanoma accounts for only a small portion of skin cancer but it is associated with high mortality. Melanoma serum biomarkers that may aid early diagnosis or guide therapy are needed clinically. However, studies of serum biomarkers have often been hampered by the serum interference that causes false readouts in immunological tests. Here we show that, after using a special buffer to eliminate the serum interference, IL-8 and cathepsin B levels were significantly elevated in melanoma patients (p < 0.05). More importantly, the combination of IL-8 and cathepsin B were also studied as a prognosis marker for melanoma mortality. Our study provides a novel approach to examine serum biomarkers.