Progesterone (PR) and oestrogen (ER) receptors were examined in meningiomas from 36 patients, using immunocytochemistry. The present experiments were performed to evaluate: (a) the presence and intracellular localization of these receptors, (b) whether PR immunostaining can be correlated (or not) with proliferation potential, as evaluated by histopathological features or the clinical evolution of this neuropathological tumour. Twenty six tumours (72%) tested were positive for PR but none for ER. The presence of PR immunostaining was more frequently observed in females (79% versus 58% in males) and premenopausal status (84% versus 3/5 in postmenopausal). Correlations of PR immunostaining with the histologic type showed 89% of meningothelial, 4/6 cases of transitional, 1/3 case of fibroblastic and 1/4 cases of anaplastic meningiomas to be immunostained for PR. Staining was confined to tumours arachnoidal cells. A heterogeneous distribution was observed in most PR-positive meningiomas. The preferential immunostaining in meningothelial histological types correlates with the presence of PR in normal arachnoidal cells. The proliferating potential of these meningiomas was evaluated by the immunostaining of an antigen only present in proliferating cells (Ki antigen). There was no significant correlation between PR status and the Ki labelling rate, or rapid clinical evolution. These data were compared with those previously reported. They confirm that the cellular biosynthesis of PR in meningiomas is not oestrogen regulated as it is in other sex steroid tissues, such as the breast and the endometrium.