Abstract Two trials with Holstein heifers evaluated their ability to meet phosphorus requirements from natural feedstuffs and the adequacy of minimums for phosphorus recommended by the National Research Council in 1974. Thirty-eight Holstein heifers were used in a 364-day study in Trial I and 28 heifers in a 238-day study in Trial II. Treatments were all phosphorus from natural feed-stuffs, and sufficient dicalcium phosphate to increase phosphorus .10% in dry matter of the total ration. All feeds, except pasture forage, were supplied as complete mixed rations. Supplementation of natural feedstuffs with .10% phosphorus had no significant effect on weight gains, efficiency of converting feed to gain, calcium and magnesium in blood serum, and conception rate. Animals supplemented with phorphorus in Trial II maintained higher phosphorus in blood serum than unsupplemented animals. Calcium, phosphorus, and magnesium in blood serum were within normal limits for both groups. Average daily gains were 721 and 745g for the two groups in Trial I and 821 and 789g in Trial II. Addition of .10% phosphorus to natural diets containing approximately .22% phosphorus had no effect on animal health or production. The minimum amounts of phosphorus suggested by the National Research Council are adequate for growing dairy heifers.