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According to recent theory on the structure of melanin, the sulfur content of melanin is a reflection of the amount of cysteine used in its manufacture. We compared the sulfur contents of melanins from hair, choroid, iris, and retinal pigment epithelium from black-haired cattle and separately from red-haired cattle. In black-haired cattle, sulfur contents of hair and ocular melanins were all between 0.60% and 0.94%, however, in red-haired cattle, hair melanin had a sulfur content (8.66%) different from those of choroid (0.94%) or RPE (1.72%) MELANIN. One may conclude that in an individual animal, ocular melanins can have different chemical structures from hair melanins. The clinical importance of this finding is discussed with regard to sympathetic ophthalmia.