objectives: to study the factors involved in the maintenance of exclusive breastfeeding in healthy infants during the first 4 months of life, with emphasis on the role of pediatricians. material and methods: a longitudinal study was carried out with 101 healthy term babies at a pediatrics outpatient clinic in uberaba, state of minas gerais, brazil. the babies were divided at random into three groups: g1, receiving advice from a multiprofessional breastfeeding team; g2, receiving advice from a pediatrician trained in breastfeeding; and g3, receiving advice from a pediatrician with no breastfeeding training. group randomization was confirmed by analysis of variance. the factors involved in the type of feeding at 4 months were analyzed by the chi-square test, by analysis of variance and by multiple variable analysis. results: at the end of follow-up, groups 1 and 2 showed similar percentages with respect to exclusive breastfeeding. in addition, the percentage of exclusively breastfed babies in groups 1 and 2 was significantly higher than in group 3 (p = 0.002). the use of a pacifier was negatively correlated with exclusive breastfeeding (p = 0.003). more maternal schooling increased the chance of exclusive breastfeeding at 4 months (p = 0.041). conclusion: in this study, a pediatrician who was prepared and motivated to encourage breastfeeding performed similarly to a multiprofessional breastfeeding team in terms of promoting exclusive breastfeeding until 4 months, a fact that was not observed when the pediatrician did not show this motivation. higher maternal schooling was associated with a higher frequency of exclusive maternal breast-feeding at 4 months, whereas the use of a pacifier favored early weaning.