Two cell lines, OCM-1 and OCM-2, were established from biopsied specimens of choroidal melanomas of spindle B and mixed cell type morphologies. Both cell lines were phenotypically malignant. Karyotypic analyses revealed human chromosomes with a modal number of 95 and 85, respectively. These cell lines have been passaged for over 2 years and are essentially immortal. The cells grew without contact inhibition as monolayers in liquid culture or as clones in soft agar. Electron microscopy revealed melanoma cells containing premelanosomes and cultures free from contamination by fibroblasts. To categorize the morphologies of these cultured cells better by the Callender classification, they were grown as xenografts in the anterior chambers of rabbits immunosuppressed with daily i.m. doses of Cyclosporin A (10 mg/kg). Tumor plaques were detected after 10 days. The eyes were enucleated and fixed in formalin and stained with hematoxylin and eosin for histopathological evaluation. The xenograft from OCM-1 was found to consist predominantly of spindle B-type melanoma cells. In contrast, the xenograft from OCM-2 contained epithelioid, spindle B and clear cell ("balloon") melanoma cells. The ability of these cell lines to grow as xenografts confirmed their neoplastic origin. In fact, the types of the uveal melanoma cells in the xenografts resembled those in the original biopsied tumors. This suggests that the morphology of human uveal melanoma cells is an inherited trait and may be genetically fairly stable.