&NA;The present study describes the phenotypic and functional analysis of tumor‐infiltrating lymphocytes isolated from a germinoma located in the pineal region. Tumor‐infiltrating lymphocytes were separated from the germinoma and cultured in medium containing IL‐2 (1000 U/ml). An immunohistochemical analysis of frozen sections revealed that 90% of the germinoma‐infiltrating lymphocytes were CD3‐positive T cells expressing CD4, CD8, and HLA Class I and Class II antigens, but were negative for CD16, CD20, CD23, CD25 and CD14 antigens. After in vitro cultivation in the presence of high concentrations of IL‐2, the lymphocytes proliferated for 2 weeks, showing marked DNA synthesis. In addition, the lymphocytes could lyse NK‐resistant allogeneic target cells. These results provide evidence for a potential role of germinoma‐infiltrating lymphocytes in vivo, and suggest that the lymphocytes may control the growth of autochthonous tumor cells by killing those that are not restricted to the major histocompatibility complex. (Neurosurgery25:454‐458, 1989)