An eye from a patient with systemic sarcoidosis and active ocular involvement was studied by the use of monoclonal antibodies and the immunoperoxidase technique to identify the subtypes of infiltrating cells and the presence of lymphokines. Large numbers of lymphoid cells reacting with anti-pan T cell (Leu-4) and anti-T helper/inducer (Leu-3a) subsets were observed around and within sarcoid granulomas. Only rare T suppressor/cytotoxic cells (Leu-2a) were observed. B lymphocytes and plasma cells were present in a few foci. Within the granuloma, T lymphocytes, macrophages, and epithelioid cells showed membrane labeling for interleukin 2 receptors and interferon gamma. We demonstrate the in vivo expression of interleukin 2 receptors and the release of interferon gamma by mononuclear phagocytes and T lymphocytes in ocular sarcoidosis, and we theorize about the activated T helper cell-derived lymphokines in macrophage activation and sarcoid granuloma formation in the eye.