This study was initiated to evaluate the effect of early expression on the bacterial colony count of human milk. Significant bacterial contamination ($10,000 colony-forming units/ml milk) was more common in 11 mothers who delayed the onset of expression of their milk compared with mothers who began to express their milk in the immediate postpartum period (n = 15) or who began to nurse their own full-term infants soon after delivery (n = 9). These data suggest that mothers who are separated from their prematurely born or sick infants should begin to express milk for their own infants as soon after birth as possible to provide milk with low bacterial contamination for frozen storage and later use.