Experiments concerning the nitrogen metabolism of 3-, 5-, 7-, 9-, and 11-week-old calves were carried through. The calves were daily fed 146, 219, 323 g milk replacer and differing amounts of dried skim milk (697, 761, 717, 723, 653 g). Energy consumption was dependent on the consumption of milk replacer. With increasing age, N-digestibility and N-retention from the feedstuffs diminished gradually. The smallest decrease of N-retention was observed with those animals receiving the highest amount of milk fat energy. The decrease of nitrogen digestibility can be attributed to the higher consumption of plant feedstuffs and the decrease of the biologic value of the protein. The experiments concerning the nitrogen metabolism show that a higher dosage of fat had a favourable influence on nitrogen retention. At an age of between 7 and 9 weeks correlation coefficients of between +0.50 and +0.36 were ascertained between the fat content of the feed ration and nitrogen retention. At the same age correlation coefficients of +0.60 resp. +0.53 were ascertained between the energy content of the ration and nitrogen retention. These investigations are the basis for the statement that for the nitrogen retention of calves at the age of 7 to 9 weeks feed energy (fat) is the most important factor. A close positive correlation could be observed between the crude protein consumed with the feed ration and the amount of digested nitrogen. Moderately positive correlation coefficients were calculated between the amount of nitrogen taken in resp. the amount of digestible nitrogen and the assessed amount of nitrogen at the age of 7, 9 and 11 weeks. The experiments with the nitrogen metabolism are the basis for the statement that protein and fat together determine the amount of nitrogen retention for calves fed wth moderate milk protein. For calves fed with less milk protein, 23 to 34% fat in the dry matter of the milk replacer proved to be successful. The favourable effect of a higher amount of milk replacer on nitrogen retention can also be attributed to the higher amount of chemotherapeutic sustances (vitamins, antibiotics) taken in with the milk replacer.