A population study of 758 infants born at the same hospital showed that weight at the ages of six week and six months was not significantly related to breast or bottle feeding, the early introduction of solids, or the sodium content of bottle feeds. Weight at six weeks was related to the volume and energy content of the feeds which were examined in those bobies that were bottle-fed alone. Although analysis of a single feed showed that mothers mixed feeds incorrectly, there was no evidence that mixing of overstrength feeds leads to obesity.