The aim of this study was to define the range of the menstrual blood loss(MBL), and the upper limit of the MBL associated with iron deficiency anemia in Korean women, For this purpose, healthy unmarried women between the age of 15 to 26 years were selected from July to September, 1979 and results obtained were used for determining baseline MBL and its relationship to iron nutriture. One houndred forteen women were tested for their MBL and hematological and biochemical data such as hemoglobin(Hb) concentration, hematocrit, mean corpuscular hemoglobin concentration(MCHC), and serum iron and ferritin concentration. This study was partly supported by World Health Organization. The results of this study are summarized as follows: 1) The mean values and standard error of mean of MBL were $30.7{pm}2.19ml$ for total subjects, $30.4{pm}3.14ml$ for sutjects below 20 years of age and $30.3{pm}2.49ml$ for subjects aged more than 20 years. No significant variation was noted for amount of MBL between two age groups. 2) The median value and 95th percentile value of MBL were 26.5ml and 69.0ml respectively for total subjects. Maximum number (24.6%) of the subjects fell in group with 10-20ml of MBL while 10.5% showed MBL above 50m1. 3) Mean value of the duration of menstruation for total subjects was 4.34 days. 4) It was observed that mean values of Hb concentration, hematocrit and MCHC were decreased slightly in subjects showing MBL more than 40m1. Serum iron and ferritin levels were markedly decreased in women with MBL above 40m1 and 20-30ml, respectively. 5) In subject population showing MBL above 50ml, the frequency of subjects with hematological and biochemical data below anemia criteria were remarkably increased. 6) Although the number of subjects tested was small and the subject selection was not done by random stratified sampling from a population group, this study suggested that the upper normal limit of MBL of Korean women seems to be in the range of 40-50ml.