Nutritional iron deficiency was produced experimentally by raising newly hatched chicks on an iron-deficient diet for several weeks. During this time, hematocrit and hemoglobin values declined, iron stores were depleted, and the circulating level of transferrin increased 2- to 4-fold. The increase in serum transferrin was related to a similar increase in the rate of transferrin synthesis in liver. In addition, the level of transferrin mRNA sequences, as determined by hybridization to a specific cDNA, increased 2- to 3-fold, and more than 80% of the transferrin mRNA was associated with polyribosomes in both control and iron-deficient liver. These results demonstrate that the induction of transferrin synthesis in iron-deficient chicks is regulated directly by an increase in transferrin mRNA. The iron-mediated effects on transferrin also appear to be gene-specific since the rate of synthesis of serum albumin, the major secretory product of liver, was unaffected by any of the experimental conditions. Furthermore, when iron stores were rapidly replenished by the administration of iron-saturated ferritin, both the rate of transferrin synthesis and the level of transferrin mRNA returned to control values with 2 to 3 days.