The primary objective of this study was to investigate the correlation between fibrinolytic activity in menstrual fluid and total menstrual blood loss during menstruation. We also wanted to evaluate the influence of desmopressin nasal inhalation on the local fibrinolytic activity in menstrual fluid. Six women with objectively verified menorrhagia and six women with normal menstrual blood loss were examined. With a slender catheter introduced through the cervical canal, menstrual fluid was collected on the day in the cycle when the most intense bleeding occurred. The fibrinolytic activity in menstrual fluid was measured both as plasmin content using an amidolytic method with chromogenic substrate and with a fibrin plate method. A significant correlation between the amount of menstrual blood loss and fibrinolytic activity was found in menstrual fluid of both groups and with both methods. We could not find an increased fibrinolytic activity in menstrual fluid when the women with menorrhagia were treated with desmopressin nasal inhalation. Knowledge of the local factors influencing monthly blood loss can be valuable when searching for more effective medical treatment of menorrhagia. Apprehension that desmopressin should increase local fibrinolytic activity in menstrual fluid could not be confirmed.