There is a need for noninvasive, low-cost, efficient methods of tagging large numbers of aquatic animals. For example, improved tagging methods are needed to follow the migratory patterns of some endangered salmonoid species. This talk reports on an investigation of the feasibility of using cavitation levels of ultrasound to mediate the delivery of tagging compounds into fish. Two tagging compounds are investigated: calcein (Fluorexon) and oxytetracycline-hydrochloride (Terramycin). Both of these compounds are presently used as tagging agents. However, injection methods of delivery are not efficient for cases where large numbers of wild fish are involved, and if they are placed directly into the aquatic environment of fish the compounds diffuse too slowly through the skin to adequately tag the fish before creating other health problems for them. A system for generating controlled doses of cavitation level ultrasound to schools of fish will be described and measurements of the enhancement in delivery of the tagging compounds to the fish will be reported.