Yellow Floy FD-67 internal anchor tags were utilized in an experimental and field study of tag discoloration, tag legibility and fouling organisms. Most tags exhibited some degree of discoloration over time. The rate and extent of discoloration varied between two batches of tags purchased in different years. The legibility of a tag was not affected to a great extent by the degree of discoloration. Legends of some completely discolored tags were still readable. Fouling organisms eroded the vinylite covering and deteriorated the legends of some tags. Bryozoans, barnacles and tunicates were the most commonly encountered fouling organisms. Barnacles were the most erosive of these organisms. Other causes of tag discoloration were believed to be chemical reactions between the vinylite covering and environmental factors such as salt concentration.