In vitro cultured human uveal and skin melanoma cells were injected into the chicken embryonal eye at a stage when the immune system was not yet mature. The melanoma cells were accepted as part of the organism by the host. Even single melanoma cells could be traced by morphological methods as well as by immunohistochemical markers, such as S100, HMB-45, NKI/C3 and HNK-1. We found tumors in 20 and 40 percent of the embryos injected with uveal melanoma and skin melanoma, respectively. The embryos did not exhibit abnormal development of the eye as a result of the microinjection and had a high survival rate (90 and 60%, respectively) during embryogenesis. With this model for uveal melanoma the growth and possibly the metastatic behavior of human uveal melanoma cells can be studied.