Mean gill burst duration during last 3 min of normoxia,10, 60, 90, 120, 150, and 180 min of hypoxia, and 30 min of normoxic recovery in control and nicotine- or ethanol-exposed early (A) and late (B) metamorphic tadpoles. 10-wk nicotine or ethanol exposure had no effect on lung burst duration. Hypoxia had no effect on gill burst duration of any early or late metamorphic tadpole treatment group. Data presented are mean ± SE for 6 –7 tadpoles (P > 0.05).