Serological markers of malignant melanoma have failed to provide prognostic significance in patients who are tumour-free after surgery. Immune response regulation is important regarding progression and therapeutic interventions of malignant melanoma. Matrix metalloproteinase (MMP)-8 is one of the collagenases involved in the regulation of tissue remodelling and immune response, being incompletely studied in melanoma as yet. We assessed whether serum MMP-8 is of prognostic value in malignant melanoma. We studied serum samples of 117 patients, of which 63 were stage I, 13 stage II, 12 stage III and 29 stage IV. The mean serum MMP-8 levels (47.5 ng/ml) did not significantly correlate with patient or tumour characteristics, that is, patient sex, age, tumour Clark's or Breslow's classification, sentinel lymph node status or to survival. Importantly, high serum MMP-8 levels were significantly related to presence of vascular invasion (P=0.001) in primary tumour, tumour ulceration (P=0.003) and tumour bleeding (P=0.033). Tendency to increased serum MMP-8 levels in patients with coronary heart disease or type II diabetes mellitus was detected. These data imply that high serum MMP-8 level is associated with earlier recognized histopathology markers of melanoma progression. Results also suggest that elevated serum MMP-8 might be related to haematogenous spreading of melanoma through vascular invasion.