Human endometrium changes morphologically and biochemically during the various phases of the menstrual cycle, influenced by not only estrogens and progesterone, but probably also by androgens. The purpose of this study was to investigate the androgen receptor (AR) content in human endometrium and myometrium and its significance. AR immunocytochemistry was performed on 30 paraffin-embedded uterine sections of pre-menopausal women who were scheduled for hysterectomy because of benign gynaecologic abnormalities. AR receptor content was seen in all cell types of the human endometrium and myometrium and was cyclic dependent. AR immunostaining of stromal and smooth muscle cells was more profound than AR staining of glandular cells. There was more AR expression in the proliferative phases than in the secretory phases: in the late secretory phase there was no immunostaining in any of the cell types. AR expression is primarily under androgenic control. Inside the cell testosterone may be 5 alpha-reduced to dihydrotestosterone (DHT). Due to local competition between testosterone and the excess of progesterone in the secretory phase for the same iso-enzyme 5 alpha-reductase, the level of DHT will be diminished in the late secretory phase. If AR synthesis in endometrium would be DHT dependent, the virtual disappearance of DHT would explain the lack of AR expression in the late secretory phase. Whether the cyclic pattern of AR expression is merely an epiphenomenon to progesterone production, or whether androgens play a causal role in the cyclic modulation of endometrium is subject to further research.