Infants need to develop effective, secure attachment to their primary caregivers in the first year of life. Researchers have not been able to identify all the factors that may influence the development of infant attachment. Most of the studies in this area have been done without regard to infant feeding as a potential factor. Maternal responsiveness appears to be key in the child's development of secure attachment behaviors, yet even after decades of research on infant attachment and maternal responsiveness, there is little evidence available to assist with early identification of families at risk and few interventions known to be effective in promoting maternal responsiveness.The research questions for this study were: 1) Do mothers who exclusively breastfed their infants for at least 6 weeks report more maternal responsiveness behaviors 2-4 months after delivery compared to mothers who exclusively formula feed their infants? 2) How well does breastfeeding duration predict self-reported maternal responsiveness at 2-4 months once socio-demographics and maternal characteristics (i.e., self-esteem, satisfaction with life) are statistically controlled?A cross-sectional survey design was used to assess the variables of maternal responsiveness, feeding patterns, and maternal characteristics in a convenience sample of 200 mothers in the first 2-4 months after delivery. The 60-item instrument included scales to measure maternal responsiveness (MIRI: Amankwaa et al., 2002), self-esteem (RSE: Rosenberg, 1965), and satisfaction with life (SWLS: Diener et al., 1985) as well as infant feeding and socio-demographic questions. A mixed mode data collection strategy was used combining Internet data collection with traditional paper-and-pencil survey methods.Somewhat surprisingly, mothers who exclusively breastfed for at least 6 weeks did not report any more maternal responsiveness behaviors compared to mothers who formula fed their infants. Hierarchical multiple regression analysis revealed that satisfaction with life, self-esteem, and parity, but not breastfeeding, explained a significant portion of the variance in self-reported maternal responsiveness scores. Further research in this area is needed. It should be noted that this is one of few studies of maternal responsiveness using a self-report instrument and may also be the first study of maternal responsiveness using Internet data collection.