The function of mast cells (MC) in human uterus is not well understood. They are found in the connective tissue of the uterus and contain very active biological substances which are able to contract smooth muscle cells. This study was undertaken to study mast cell count in praemenopausal and postmenopausal uterus. Tissue samples were obtained from uteri at hysterectomy and MC numbers were quantitated in the uterine wall of patients in two groups (praemenopausal, postmenopausal). A significant correlation was found in the MC count between praemenopausal and postmenopausal patients in corpus and istmus. In the myometrium, the overall numbers failed with advancing age. In conclusion, MC count, in the case of the human uterus, might be associated with smooth muscle contraction.