In order to determine the effect of feeding glucose water on breastfeeding newborns, we randomly distributed 180 normal newborns into two groups: a glucose water group (GW), fed 5% glucose solution during the first 3 days of life in addition to being breastfed; and an exclusively breastfed nonglucose water group (NGW). The following data were evaluated: weight at 6, 12, 24, 48, and 72 hours of life; temperature during the first 72 hours of life; serum glucose level at 6, 12, 24, and 48 hours; total duration of breastfeeding and age at introduction of infant formulas. In the NGW, there was a greater weight loss at 48 hours but not at 72 hours, temperatures higher than 37.5 degrees C were more frequent, and the mean serum glucose levels at 6, 12, and 24 hours were lower. This group also had more serum glucose level determinations under 2.2 mmol/l (40 mg/dL). However, no infants exhibited hypoglycemic symptoms. Infants in the GW received twice as many formulas during the first month and had a shorter duration of any breastfeeding. Our results suggest that the suppression of feedings with glucose water in the first days of life increases the probability of successful breastfeeding. However, infants who do not receive glucose water in the first few days of life may require greater supervision and close monitoring of blood glucose and body temperature, particularly in the first 24 hours of life.