The biosynthesis of estradiol and related estrogens is catalyzed by the enzyme aromatase. Among other tissues, aromatase is expressed in the brain, where it is involved in the regulation of neuroendocrine events and reproduction. Under physiological conditions, the expression of aromatase in the mammalian brain is restricted to neurons. However, recent studies have shown that reactive astrocytes express aromatase after brain injury. This opens the possibility for the expression of the enzyme in other altered forms of glial cell, such as gliomas. In the present study, the expression of aromatase has been assessed, by RT-PCR and immunocytochemistry, in the rat glioblastoma C6 and in two human glioblastoma cell lines T98G and U373MG. The three cell lines expressed aromatase mRNA and showed a cytoplasmic pattern of aromatase immunoreactivity. In addition, the three cell lines express estrogen receptor alpha, suggesting that estradiol formed by aromatase may act as an autocrine or paracrine factor for glioblastoma cells. By analogy to the implication of aromatase into the growth of other forms of estrogen-sensitive tumors, such as some breast cancers, it is conceivable that the expression of aromatase may play a role in the growth of glioblastomas.