Osteopontin is a ligand for the integrin proteins, which are cell surface receptors that mediate the physical and functional interactions between a cell and the extracellular matrix. The expression of osteopontin is reportedly increased in a number of transformed cell lines and tumor tissues. Furthermore, increased expression of osteopontin results in some infiltrative features of tumors. The aim of the study is to demonstrate that expression of osteopontin in human astrocytomas correlates with histological tumor grade. The expression of osteopontin in human astrocytomas was determined with immunohistochemistry. Median osteopontin expression levels were 1%, 7.5%, 60%, and 50% in grade I, II, III, and IV tumors, respectively. Osteopontin staining was significantly higher in high grade (grade III-IV) than low grade (grade I-II) tumors. These findings indicate that osteopontin immunoreactivity in human astrocytomas may correlate with the grade of a tumor.