In two large maternity wards encouraging breast-feeding, breast-milk volumes (weighing of the baby before and after each feeding) and weight development of the infants were determined until dismissal. On days 2, 3 and 4, 20-30%, 60-70%, and 80-90% of the mothers, respectively, produced milk. The largest increase in milk volume ("Einschuss") usually took place between days 3 and 4. Milk volume increased from an average of 150-180 ml on day 4 to 270-300 ml on day 6. Development of milk production was independent of type of delivery; however, the usual delay of one day following caesarean section was not made up for until discharge. Fully breast-feeding mothers produced on the average the same amounts of milk as mothers at the turn of the century. Throughout their stay in the maternity ward, mothers with good breast-feeding experience produced more milk than those with bad or without any breast-feeding experience. Nursing all infants at fairly regular intervals during the day and at night is recommended in order to achieve that as many mothers as possible are fully breast-feeding on discharge. Comparing energy intake and weight development between groups of fully, partially and non breast-fed infants suggested a better utilization of breast-milk.