Activity was seen in the breasts of a patient with galactorrhea 72 h after intravenous injection of Ga-67 citrate. Differential protein separation of breast secretion, extracted from the breast, revealed that the Ga-67 was contained primarily in the lactoferrin-rich protein fraction. Additional studies on partially purified lactoferrin revealed that lactoferrin binds Ga-67 more avidly than does transferrin. Since lactoferrin is present in high concentration non only in human colostrum and milk, but also in neutrophilic leukocytes, bone marrow, spleen, colon, tears, and in genital, salivary, and nasopharyngeal secretions, binding of Ga-67 to lactoferrin may explain the localization of Ga-67 in certain normal tissues and inflammatory lesions.