To determine whether the herbicide, atrazine, affects the stress hormone corticosterone, we exposed Osteopilus septentrionalis (Cuban Treefrog) tadpoles to four concentrations of atrazine and two controls (water and acetone) for three time durations (4, 28, and 100 h). Atrazine concentration, but not exposure duration, had significant nonlinear effects on whole-body corticosterone. Relative to controls, intermediate concentrations of atrazine (10.2 and 50.6 μg/L) tended to lower corticosterone, whereas the lowest (0.1 μg/L) and highest atrazine concentrations (102 μg/L) elevated corticosterone. These results indicate that atrazine exposure might dysregulate corticosterone, a hormone integral to vertebrate immunity, neurogenesis, and health.