Progesterone receptors (PR) have been detected in human astrocytomas; however, the expression pattern of PR isoforms in these brain tumors is unknown. Progesterone receptor isoforms expression was studied in 13 biopsies of astrocytomas (6 grade III, and 7 grade IV) from adult Mexican patients by using reverse transcription-polymerase chain reaction and immunohistochemistry. Progesterone receptor expression was observed at mRNA and at protein levels in 66% and 83% of astrocytomas grade III, respectively, whereas 100% of astrocytomas grade IV expressed PR. Almost all PR mRNA content in astrocytomas grades III and IV corresponded to PR-B. The number of immunoreactive cells expressing PR-B was higher than that expressing PR-A in 73% of the cases. Estrogen receptor-alpha protein was only observed in 33% of astrocytomas grade III, whereas no astrocytomas grade IV expressed it. These data suggest that PR-B is the predominant isoform expressed in human astrocytomas grades III and IV, and that estrogen receptor-alpha is not expressed in astrocytomas grade IV.