In Temuco, Chile, 114 women in fully nursing, were studied, according to their length of lactational amenorrhea and their relation with estradiol levels at 3th postpartum month. Sixty six (58%) recovery their menses before the 6th postpartum month. The length of lactational amenorrhea was 100.7-5.2 and 277 +/- 10.6 days, for those mothers who were with menses and amenorrhea, respectively. The estradiol levels were 88 pmol/l higher in the woman with short length of lactational amenorrhea. This study corroborate, that short length of lactational amenorrhea is a condition highly frequent in Chilean population. The difference in the estradiol levels may be a indicators of the early recovery of the postpartum fertility.