Plasma lipid bound sialic acid (LSA) was measurement in 41 patients with malignant melanoma to determine the utility of this biochemical marker in the stating and in monitoring the post-operative follow-up. LSA was determined in 26 cases pre and post-operation, and in 15 cases only post-operation. Multiple determinations was done in 12 cases during two years of post-operative follow-up. Patients with preoperatory determination exhibited LSA levels significantly higher (p 0.0001) than the healthy control group. Relationship between LSA highest levels and tumoral size up 2 cm. in diameter was found (p 0.02). A second determination after 2 months of cases. LSA multiple post-operative controls showed continuing elevation of LSA levels up the normal rates was corresponding with metastasis in 100% of cases.