Annexin II is highly expressed in glioblastoma multiforme [Reeves, S. A.; Chavez-Kappel, C.; Davis, R.; Rosenblum, M.; Israel, M. A. Developmental regulation of annexin II (lipocortin 2) in human brain and expression in high grade glioma. Cancer Res. 52:6871-6876; 1992] and is a likely second messenger in mitogenic pathways known to be important for the growth of these tumors. We have examined tumor tissue from patients diagnosed with low-, intermediate-, or high-grade astrocytic tumors for expression of annexin II by immunohistochemistry, and found that annexin II levels varied significantly among these three tumors (P < 0.0005). Levels were highest in glioblastoma multiforme, intermediate in anaplastic astrocytomas, and lowest in astrocytomas. In contrast to the usual cytoplasmic localization of annexin II, distinct nuclear staining was found in many of the specimens. Reactive astrocytes found in gliotic brain also stained with anti-annexin II antibody. We examined matched specimens for a correlation between annexin II staining intensity and the bromodeoxyuridine labeling index and found that, while tumors with the most intense annexin II staining had highest bromodeoxyuridine labeling indexes, there was not a strong association between these two parameters. The association between annexin II staining and histologic grade in astrocytic malignancies indicates that annexin II may be an important marker of high-grade glial tumors, and suggests that this marker may be useful for the pathologic classification of glial tumors and the clinical evaluation of brain tumor patients.