The aim of this study was to evaluate the correlation between the detection of circulating melanoma cells and prognostic criteria for malignant melanoma such as clinical stage, tumor thickness and histological type of the primary tumor. Using a reverse transcriptase-polymerase chain reaction (RT-PCR) technique, melanoma cells were identified by detecting tyrosinase mRNA in peripheral blood from 58 patients with malignant melanoma classified according to the American Joint Committee on Cancer guidelines. The results of the RT-PCR assay for tyrosinase were related to two prognostic markers typically used to evaluate these tumors: clinical stage and thickness. Positive PCR results were more frequent in primary tumors measuring > 4 mm (83%) than in thinner tumors (1.1-4.0 mm, 74%; < or = 1.0 mm, 23%) (P = 0.005). No statistical correlation was found between the PCR results and histological appearance of the primary tumor. Although further studies are necessary, our results suggest the possible application of the PCR assay for tyrosinase mRNA in clinical evaluation of the prognosis of malignant melanoma.