BACKGROUND: Stromal leucocyte populations in human endometrium comprise T cells, macrophages, and phenotypically unusual endometrial granulated lymphocytes. Their proportions vary during the menstrual cycle and, in particular, endometrial granulated lymphocytes increase in number in the late secretory phase. The stimulus responsible for these cyclical changes is unknown but it is likely that the steroid hormones oestrogen and progesterone play a role. AIMS: To define further the expression of steroid hormone receptors by leucocytes in non-pregnant and pregnant human endometrium. METHODS: Frozen and paraffin wax embedded sections of endometrium from non-pregnant women and early pregnancy decidua were labelled using single and double immunohistochemical techniques with monoclonal antibodies directed against oestrogen and progesterone receptors and various leucocyte subpopulations. RESULTS: Despite the prominence of CD56 positive endometrial granulated lymphocytes in late secretory phase endometrium and early pregnancy decidua, double immunohistochemical labelling showed no evidence of expression of either progesterone or oestrogen receptors by these cells or other endometrial leucocyte populations. CONCLUSIONS: Rather than acting directly, steroid hormones are likely to influence endometrial leucocyte populations indirectly via products of endometrial stromal or epithelial cells that express steroid hormone receptors.