As part of the 1988 National Institute of Child Health and Human Development school-based survey of two metropolitan Washington, D.C. counties to identify children in the 1978 to 1979 birth cohort who had been exposed to the chloride deficient formulas Neo-Mull-Soy and Cho-Free during infancy, information on breast feeding was also obtained. We thus asked the question, does breastfeeding among children who had been provided soy formulas during infancy affect general health and cognitive development 9 and 10 years later. There were 213 children who received no breastfeeding (NBF) and 420 children who were breastfed (BF). The median duration of breastfeeding was 124 days with an interquartile range of 42 to 248 days. There were no differences in birth weight, gender, or race between the BF vs NBF. The mean WISC-R Full Scale IQ score was 121.0±14.6 among the BF and 117.5±14.7 among the NBF (p=0.005). There were several socioeconomic differences between the two groups. BF children had mothers and fathers with higher levels of education and higher incomes. Following adjustment by regression analysis for these factors, the WISC Full Scale IQ scores were no longer different(p=0.326). On questions that ranged from areas of information on acute ear infections to the occurrence of food allergies, no differences were observed between the two groups. These data fail to document an effect of breastfeeding on cognitive development at 9 to 10 years of age after soceioeconomic status is taken into account. In addition no differences were observed in reported health outcomes. Limitations of this analysis include the fact that these data were obtained from a highly select group of children provided soy formulas during infancy.