The aim of this study was to investigate the effects of feeding type and osmotic load on intravascular volume status. Ninety term, healthy infants 2 mo of age were included in the study. The breastfed and formula-fed groups each consisted of 45 infants. Echocardiographic examination was performed before and after feeding. The collapse index of the inferior vena cava (IVCIC) and right atrial pressure (RAP) were calculated. No statistically significant differences were found between before- and after-feeding values of IVCIC, RAP and hepatic vein velocities in breastfed infants. In the formula-fed group, after-feeding values of IVCIC were significantly lower and RAP, hepatic vein systolic and diastolic velocities were significantly higher compared to the before-feeding values. Most of the mothers (78%) were unsuccessful at preparing the formula at appropriate concentrations. No statistically significant differences were found between the before- and after-feeding values of IVCIC, RAP and hepatic vein velocities in infants being fed appropriately prepared formula. The after-feeding values of hepatic vein velocities were higher than those of before-feeding values; after-feeding values of IVCIC were lower than before-feeding values in infants being fed highly concentrated formula.