Ultrasonic transmitters were placed in the peritoneal cavity of twelve adult grass crap in a Florida reservoir. Tagged grass crap ranged in size from 3.68 kg to 12.72 kg. No mortality of tagged grass carp was observed, but some difficulty was encountered with sound reception due to heavy vegetation and thermoclines. Fish took long rest periods between moves during both day and night. They were more active during the day than at night, with water temperatures limiting activity more than any other parameter tested. Displacement ranged from 182.9 m to 18,292.6 m.