Aim: The intention of this study performed in healthy breast- and formula-fed infants was to characterize physiological feeding patterns as a basis for counseling parents to feed their infants on demand. Methods: Ingested milk volumes of 10 breast-fed and 14 formula-fed infants were measured during five 72-hour investigation periods during the 3rd, 6th, 9th, 13th, and 17th weeks of life. Results: A comparable diurnal distribution of feeds was observed in both groups during the first 9 weeks of life, with a day-night asymmetry of feeding first observed at the age of 6 weeks. Thereafter, formula-fed infants showed a further decrease in their nightly milk intake. Within the investigation period, the milk volume per feed rose from 100 (range 40–200) g to 140 (range 30–300) g in the breast-fed group and from 100 (range 20–200) g to 200 (range 20–450) g in formula-fed infants. From the 6th week of life onwards, formula-fed infants had significantly higher feeding volumes. Conclusions: Parents should be informed about the variability of infant demands per feed and of feeding at night observed in breast-fed infants. The results suggest that feeding patterns similar to those of breast-fed infants are difficult to accomplish in formula-fed infants.