19 CFR 12.17: Importation restricted.

The importation into the United States of viruses, serums, toxins, and analogous products for use in the treatment of domestic animals is prohibited unless the importer holds a permit from the Department of Agriculture covering the specific product. The port director shall notify the Animal and Plant Health Inspection Service, Veterinary Services, Washington, D.C., of the arrival of any such product, and detain it until he shall receive notice from that Department that a permit to import the shipment has been issued.