Test-weighing (TW) was evaluated in formula-fed (FF) infants by comparison with direct measurement (DM) of formula intake during a 24 h period at 1, 2, 4 and 6 mo of age. Formula intakes estimated by TW ranged from 87 to 93% of those determined by DM over the 6-mo period. During the study period the number of feedings per day decreased but were not significantly different for FF and BF infants. Volume of intake per feeding by FF infants increased significantly during the 6-mo period whereas milk intakes of BF infants were not different at the four ages studied. These data indicated that when the number of daily feedings decreased with age, FF infants increased their volume of intake per feeding whereas BF infants did not adjust their intakes. Mean volume of milk intake at 4 and 6 mo, estimated by TW, was significantly greater in FF infants compared to breast-fed (BF) infants matched for age and size. Data from this study indicated clearly that when milk intakes of BF infants are compared to those of FF infants, both groups of infants should be test-weighed.