The serum levels of the soluble form of intercellular adhesion molecule-1 (slCAM-1) and 5-S-cysteinyldopa (5-S-CD) were determined by double determinant immunoassay and high-performance liquid chromatography, respectively. Fifty-three melanoma patients (stage 1, 12 patients; stage II, 11; stage III, 19; and stage IV, 11; total number of samples, 116) and 31 age- and sex-matched healthy control subjects were analysed. Both the slCAM-1 and 5-S-CD levels were significantly higher in stage IV patients than those in stage I, II and III patients (slCAM-1; all P<0.001; 5-S-CD; all P<0.05). The serum levels of 5-S-CD were elevated only in stage IV patients. slCAM-1 levels elevated gradually with disease progression. Testing of sequential bleedings showed that both slCAM-1 and 5-S-CD levels were elevated in most of the patients whose disease had progressed. However 5- S-CD levels were not elevated in those patients whose metastases were amelanotic. There was a statistically significant correlation between slCAM-1 and 5-S-CD levels (R=0.6 55, P< 0.001). Serum levels of 5-S-CD may be a useful parameter for monitoring the clinical course of the disease in patients whose metastases are melanotic. Analysis of both slCAM-1 and 5-S-CD levels in serum will contribute greatly to monitoring the clinical course of melanoma patients.