Determination of blood tyrosinase mRNA by RT-PCR and markers of tyrosinase activity (L-DOPA/L-tyrosine ratio) by HPLC have been proposed as biological tools for the detection of metastases in melanoma patients. We prospectively evaluated their significance and clinical value in a group of 30 stage III (n = 10) and IV (n = 20) melanoma patients and one with melanosis of Dubreuilh. L-DOPA/L-tyrosine ratio was elevated in 30% of stage III, 41% of stage IV patients (range: 7.5-261.0 x 10(5)) and in melanosis of Dubreuilh (184.8) (reference values: 6-16 X 10(5)). One stage III and four stage IV melanoma patients were positive for tyrosinase mRNA. In stage IV patients, tyrosinase mRNA positivity was associated with disease progression (P<0.01). The presence of tyrosinase mRNA in blood is more related to clinical status than level of melanin precursors, which probably reflects tumor burden.