• Monoclonal antibody MAb8-1H, which defines an ocular melanoma-associated antigen retained in fixed tissue, was used to demonstrate metastatic melanoma cells in liver biopsy specimens from five patients with primary choroidal melanoma. In all cases, the monoclonal antibody bound to tumor cells and not to normal hepatocytes. In one case, a welldelineated focus of tumor cells bound to MAb8-1H; in two cases, MAb8-1H appeared to delineate individual tumor cells that were difficult to categorize by conventional staining techniques. The liver biopsy specimens were almost completely replaced by tumor cells in the remaining two cases. This monoclonal antibody may be applicable to the diagnosis of metastatic uveal melanoma and to delineate micrometastasis.