Six groups of Holstein male calves, 4–5 days of age, were fed milk replacers containing, on a dry matter basis, 24.8% of either butter oil, lard, lard and corn oil (2:1), hydrogenated corn oil, or corn oil. Whole milk was used as control and the experiment lasted 56 days. The calves were fed, twice each day, a milk replacer containing 13% solids which was offered at a maximum daily rate of 12% of body weight as measured weekly. On the 28th and 56th day of the experiment, blood samples were drawn from the left jugular vein before the morning meal, and then 1, 2, 3, 4, 5, 7, 9, 11 and 13 h after feeding. Dry matter intake and growth rate were the lowest with calves receiving the corn oil diet. The calves fed corn oil also exhibited more frequent diarrhea. The vegetable fats, as compared to the animal fats, tended to induce a lower concentration of essential amino acids in blood plasma, but this trend was not statistically significant [Formula: see text] in all cases. The concentration of nonessential amino acids followed the same general trend as noted with essential amino acids. The concentration of total amino acids was the lowest for calves fed corn oil. Amino acid levels in blood varied with time after feeding, and exhibited postprandial patterns that differed from one amino acid to another or one group of amino acids to another. It would appear that type of dietary fat, under the conditions of this experiment, had an influence on amino acid metabolism in the young calf.