A selected group of 12 breast-fed infants were studied for insensible weight loss over the first year life. The method used to determine the insensible weight loss was non-invasive and based on a computerized weighing system. Findings indicate that the insensible weight loss in a one-year-old child reaches 36% of the average insensible weight loss reached in adulthood (360 g/day). Furthermore, the insensible weight loss (g/h/kg) was constant at about 1.9 g per kilogram per hour over the first year of life. Insensible weight loss contains two components, insensible water loss (92%) and metabolic losses (8%).