Purpose: To identify sialic acid as a tumor marker to be used in experimental models. Obtained data will be extrapolated to humans, so that this marker can be used in clinical practice. Materials and methods: We used B16 melanoma cells. The lot was composed of 30 male C57Bl6 mice, which received subcutaneous injections of 5x105 B16 melanoma cells into the right flank. Tumor volume was measured with a vernier caliper. Sialic acid was determined from the serum obtained by cardiac puncture. The second step of our research was performed on a number of 25 patients with cutaneous melanoma. Determination of sialic acid was performed using the Kattermann colorimetric method. The correlation between sialic acid and disease progression was exemplified in two clinical cases. Sialic acid determination was performed dynamically from diagnosis, following disease progression. Results: In murine models tumors increased after a lag period of up to 10 days. Tumor growth was recorded by measuring the tumor’s diameters and calculating its volume. We observed a progressive increase of sialic acid in parallel with tumor volume. In human subjects, sialic acid levels increase in metastatic disease and are common in localized disease. In the two clinical cases there was a very strong correlation between sialic acid and disease progression. Conclusions: B16 melanoma cells are highly metastatic. Sialic acid level was increased in metastatic tumor animals compared to normal animals. Higher levels of sialic acid have been shown to correlate with the metastatic potential of tumor cells. For humans, determination of total serum sialic acid would be more useful for diagnosis of advanced melanoma stage rather than for early detection and screening.