Nine young American alligators (Alligator mississippiensis) were injected at monthly intervals with tetracycline to determine the bone apposition rate and the resorption patterns over a 3-mo period. The periosteal apposition rate increased progressively over the 3-mo period from 2.99 μm/day to 5.94 μm/day. Endosteal apposition rate was much slower with incomplete tetracycline lines being observed on the endosteum. This suggests that most modeling-resorptive activities occur on the endosteal envelope.