1. After transfer of the freshwater-maintained ducks to a hypertonic saline regimen the wet weight, the protein content and the RNA content of the nasal glands showed a two-fold increase.

2. The RNA content of the nasal glands was maximal after approximately 24 hr. whereas the maximum wet weight and protein content did not occur until after approximately 14 days of exposure to hypertonic saline.

3. The DNA content of the nasal glands increased by approximately 42% during the period of adaptation to hypertonic saline and at the same time the weight of gland per unit DNA increased by about 58%.

4. The wet weights, nucleic acid concentrations and the protein concentrations of Harderian glands, liver, kidney and adrenal glands did not change upon adaptation of the ducks to the hypertonic saline regimen for 14 days.

5. Upon return of the birds to the freshwater diet, the weight, protein content and RNA content of the nasal gland declined. No loss of DNA was apparent. The weight of the gland per unit DNA and the protein content per unit DNA and the total RNA content of the nasal glands all returned to the level observed in the freshwater-adapted birds.

6. When the birds were again transferred to the hypertonic saline diet the nasal glands returned to the state of development previously observed when the birds were maintained on the hypertonic saline regimen.

7. The significance of these data in relation to the changes known to occur in the active sodium-transporting properties of the nasal gland are discussed.

This work was supported by research grants to W.N.H. from the National Science Foundation (Grant no. GB 3896) and the Committee on Research, University of California.
 N.D.E.A. (Title IV) pre-doctoral fellow.