Caseins are a mixture of related phosphoproteins occurring in milk and cheese. The group is characterized as one of the most nutritive milk proteins, containing all of the common amino acids and rich in the essential ones. Iodine is a nutritionally essential element, especially important in thyroid hormone synthesis. In dogs, iodinated casein is indicated for apparent decreased thyroid activity where the signs are alopecia, scaliness of the skin surface, loss of hair, seborrhea, thickening of the skin, hyperpigmentation, and lethargy. If no response is observed in 30 to 45 days, the drug is usually withdrawn and the diagnosis reconsidered.