The record of 50 postpartum women who intended to breast-feed for longer than 6 month were analyzed. Fifty percent of the women breast-feed longer than 12 month, and 50% resumed menses by 40 weeks after childbirth. Fifty-two women record of mucus and basal body temperature (BBT) fort at least 4 week before resumption of menses. Ovulation before menses while fully breast-feeding was probable in only one woman. Fifty percent of the first postpartum cycles had a short luteal phase Thirty-five women chose NFP to avoid pregnancy during the study period. Mucus and BBT proved to be a good marker of ovulation during postpartum cycles. Confidence in NFP during lactational amenorrhoea and first postpartum cycles in analyzed. Finally, research aimed at improving the teaching and use of NP for postpartum breast-feeding women is described.Two longitudinal studies of breast feeding behavior were conducted in a sample of Romanian women from rural Chisinau and Iasi in 1991. Daily records were maintained of suckling patterns, supplementary feeding, illness, cervical mucus, basal body temperatures, and coital frequency. The sample included 180 mothers, of whom 50 provided complete records. 31 mothers provided blood samples for hormonal analysis of the return of menses. The sample age averaged 25 years. Women had one to five children. 55% had completed some tertiary education. The mean birth weight of infants was 3325 g. 35 couples used natural family planning methods throughout the study period. 50% of mothers breast fed longer than 12 months. The average age for beginning of supplementation was 20.4 weeks after delivery. Menses returned by 40 weeks after delivery for 50% of mothers. Supplementary feeding was unrelated to the return of menses. Of the 52 women, who kept records with mucus and basal body temperature, 17 reported evidence of ovulation with a normal luteal phase before menses. 10 cases were confirmed by hormonal testing. Only 1 mother was fully breast feeding when the ovulation probably returned, based on a mucus observation. 35% of mothers showed evidence of normal ovulation before first menses. 52 weeks postpartum was the mean for return of ovulation. By the 7th cycle, all women had normal ovulation. 20 of the 34 couples practicing family planning had resumed intercourse within the first 6 weeks after delivery. Frequency of intercourse did not vary over the period of amenorrhea. 87% felt comfortable using natural family planning, although 50% had difficulty in at least one cycle. No pregnancies occurred before first menstrual bleeding among breast feeding mothers or mothers who had weaned their babies. Education should be provided to breast feeding mothers regarding the signs of returning fertility, as an additional tool in use of natural family planning.