Child spacing is achieved among many tribes of Zaire through the practice of prolonged lactation and not extended postpartum abstinence. In the Great Lakes region of Central Africa postnatal abstinence is unknown and sexual intercourse takes place 5-6 days after delivery. Still the ideal of having children spaced at intervals of 3 years exists in practice. This study shows that in traditional rural areas birth intervals can reach durations as long as 37-38 months. In the rural areas influenced by monetary income and western acculturation and influence, birth intervals are 30-32 months. In urban settings birth intervals are 25-26 months. This decline in birth intervals does not lead to a conscious behavior to delay pregnancy; it is simply the result of a different mode of life, more akin to that of western civilization. Birth interval variations are correlated with duration of postpartum amenorrhea, which changes from 19 months in rural settings to 9 months in urban settings. Up to date observations do not explain this phenomenon. 2 hypotheses are discussed. The 1st one suggests that the shorter urban duration of postpartum amenorrhea is due to changes in breastfeeding patterns. However, the 19 month amenorrhea in rural setting is unexplained by the effect of lactation. The 2nd hypothesis is that moderate chronic malnutrition, characterized by unbalanced supplies in protein and lipid, is the factor responsible for prolonged duration of postpartum amenorrhea. On the other hand, the nature of available data does not allow for an interpretation of the length of postpartum amenorrhea in the Ngweshe region, where the nutritional supply is worse than elsewhere.