Recent studies examining oestrogen and progesterone receptor status and the proliferative activity of endometriotic lesions have produced conflicting reports. This study aimed to clarify the receptor status and proliferative activity of eutopic and ectopic endometrium from women with endometriosis and endometrium from normal women. Progesterone and oestrogen receptor expression and proliferative activity were studied in eutopic and ectopic endometrium from 30 women with endometriosis and in endometrium from 30 normal cycling women using microwave-pretreated paraffin-embedded sections stained with an avidin-biotin peroxidase technique. Progesterone and oestrogen receptor expression in the control endometrium did not differ from that of eutopic endometrium from women with endometriosis. Oestrogen receptor expression in ectopic endometrium increased from the proliferative to the late secretory phase. Epithelial progesterone receptor expression decreased during the cycle. Oestrogen receptor expression in both epithelium and stroma of ectopic endometrium was significantly higher than in eutopic endometrium throughout the cycle. In contrast, stromal progesterone receptor expression tended to be reduced in ectopic endometrium compared with eutopic tissue. Epithelial progesterone receptor expression was increased in ectopic endometrium but only in the late secretory phase. Although proliferative activity in the epithelium of control and eutopic endometrium was reduced from the proliferative to the late secretory phase, stromal activity did not vary. The proliferative activity in ectopic endometrium remained low and constant throughout the cycle. In the proliferative and early secretory phases, the proliferative activity of eutopic endometrium was increased compared with ectopic endometrium, but in the late secretory phase, levels were comparable. These findings challenge previous reports which have suggested that oestrogen receptors are reduced in ectopic tissue. This may have clinical implications for the development of novel treatments for endometriosis.