Using data from Mexico's Demographic and Health Survey, the authors examine the effects of breast-feeding and the pace of childbearing on early childhood mortality in a sample of 2,665 children born between 1982 and 1986. From a family planning perspective, they seek to assess the impact that changes in childbearing patterns and associated changes in breast-feeding patterns may have on infant and childhood mortality. This is done by integrating breast-feeding models with variables influencing the pace of childbearing. The analysis indicates that the effects of breast-feeding on infant mortality were strong, consistently negative, and statistically significant until at least the sixth month of life, after which they were considerably diluted. Among the other variables analyzed, the effects of a following conception on mortality were found to be very strong among infants 3-5 months old; and maternal age at delivery appeared to have some importance among infants 1-2 months old and among children in the second year of life. To examine likely interactions between family planning, breast-feeding, and mortality, an integrated model was applied that simultaneously considered these and a range of other variables. The results suggest that the effects of improved birth spacing and maternal age at delivery associated with family planning are powerful enough to cause 20-40% reductions in infant mortality. However, the effects of reduced breast-feeding associated with family planning are great enough to offset more than 60% of these benefits. Limitations of the model make it necessary to emphasize that all of these conclusions need to be accepted with caution.