Construction of a flexible plastic cllar for marking geese is described. The usefulness of the collars, tried on 468 Canada geese (Branta canadensis) at the Seney National Wildlife Refuge from 1963 to 1965, was compared with that of nasal discs attached to 361 Canada geese at Seney in 1961 and 1962. The collars were superior to the discs in visibility, retention, and ease of placement, and injury to the geese was eliminated. There was no evidence that the collars affected breeding behavior.