Serum hepatic cell-surface enzymes, isoenzymes, and sialic acid levels may be useful adjuncts in detecting early metastatic disease and in evaluating the tumor burden of patients with uveal melanoma. Hepatic cell-surface enzyme concentrations were elevated in the serum of ten patients with uveal melanoma and liver metastasis and in five patients with other hepatobiliary disorders and in 75 control patients. Five patients in the metastatic group (50%) had serum gamma-glutamyl transpeptidase and 5'-nucleotide phosphodiesterase (5-NPD) bands known to be associated with either primary hepatic carcinoma or carcinoma metastatic to the liver. One patient with uveal melanoma without known metastasis had a positive 5-NPD pattern; metastatic disease was subsequently proved. Higher levels of sialic acid were found in the serum of patients with uveal melanoma and metastatic disease (4 mumole/mL) than in controls (2.4 mumole/mL).