The Tennessee Aquarium began using Passive Integrated Transponders during 1995 as a means identifying individual specimens within very large and complex exhibits. Previously employed methods of identification, such as marginal notching in turtles, have displayed a variety of problems. A Trovan reader, charger, implanter and one hundred ninety transponders with bar-code labels were purchased from InfoPET Identification Systems, inc., Burnsville, MN. during late 1994. The primary reason for acquiring the transponders was to identify individual turtles within two of the aquariums largest exhibits, Delta Country and Nickajack Lake. The success achieved within these two exhibits has led us to broaden the use of transponders to include portions of the lizard, fish and soon the amphibian populations within the aquarium. To date a total of 250 transponders have been implanted in 35 species, consisting of 17 genera. We have used the standard implant locations established by Susan B. Elbin, Research Associate, Ornithology Department, Society for Wildlife Conservation, Bronx, New York. Animals implanted have varied from .05 to 63.5 Kg in weight. Fewer than ten percent of the transponders implanted have been recorded as shed or lost. However three animals have lost transponders repetitively. Refinement of the technique used has decreased both the initial and recurring loss of implanted transponders. It appears that their use can be a very effective solution to identifying individuals within large groups of animals.