Among many studies on the health effects associated with lead burden in human, none has addressed for menstrual cycle. Studies have reported that blood lead levels (BLLs) may increase as estrogen levels decrease. We conducted a study to test whether the BLLs vary during the menstrual cycle. The subjects were 138 teen girls recruited at a junior nursing college. Blood specimens were collected in non-menses days in September 2003 (baseline BLLs) and during days of the menses in December 2003 (between 72nd and 96th hours of the period for follow-up measures). The paired test for differences of BLLs was used to compare between these two measures. There were no significant differences in baseline characteristics between students who had participated in both the baseline and follow-up studies and students who had participated only in baseline study. The average BLLs measured during the menses was 0.20 microg/dL higher than that measured at the baseline study (p<0.01). This finding suggests that the average BLL was 7.6% increased at the menses among these teen girl students. In the future, the time to collect blood samples for measuring lead for women should be standardized.