The metabolic responses to graded levels of exercise were determined for three species of anuran amphibians (Bufo americanus, Hyla crucifer, and Rana sylvatica). Both oxygen consumption ($\dot{V}_{O_{2}}$) and lactate production were measured at low, moderate, and high levels of mechanically stimfilated activity. Significant elevations in whole-body lactate content were observed in all three species during moderate exercise. Anaerobic threshold, defined as the $\dot{V}_{O_{2}}$ above which metabolic acidosis occurs, was estimated to be 0.47 ml O₂/(g · h) for B. americanus (45% of maximum oxygen consumption, $\dot{V}_{O_{2}}$ max), 0.56 ml O₂/(g · h) for H. crucifer (54% of $\dot{V}_{O_{2}}$ max), and 0.47 ml O₂/(g · h) for R. sylvatica (63% of $\dot{V}_{O_{2}}$ max). These values are consistent with data for other vertebrates, suggesting that anaerobic threshold is a relatively constant percentage of aerobic capacity.