Twenty-five uveal melanomas were stained with seven monoclonal antibodies (MoAbs) recognizing different antigens on cutaneous melanomas. A two step immuno-peroxidase procedure was used. Phenotypic heterogeneity was observed for four MoAbs (M.2.2.4, AMF-7, 225.28S, PAL-M1) while two MoAbs (NKI-beteb, CL203.4) reacted strongly with most (85%) uveal melanomas, and one MoAb (R-24) showed very low reactivity. Despite heterogeneity, co-expression of some antigens was observed. Expression of the antigen recognized by MoAb M.2.2.4. was significantly lowered by pre-enucleation irradiation while the other antigens remained unchanged. Expression of antigens on uveal melanomas differed markedly from primary cutaneous melanomas. The clinical relevance of these findings awaits further study.