The basis for differences in whole-body lactic acid concentrations after activity in three species of anurans was investigated. Rana pipiens and Xenopus laevis were exercised to fatigue, and Bufo boreas were kept in continuous activity for 15 min. Differences exist among the species in the ratio of muscle to body mass in the order X. laevis > R. pipiens > B. boreas. Whole-animal and hind-limb-muscle lactic acid concentrations after activity varied among species in the following order: X. laevis > R. pipiens > B. boreas. Lactic acid concentrations were similar in the sartorius muscles of the three species, but B. boreas differed from the other two species in the concentrations of lactic acid in its gastrocnemius muscles. Blood lactic acid was high in all three species, 140-200 mg/100 ml, led to a decrease in blood pH to around 7.0, and was a poor indicator of whole-body lactic acid. A total lactic acid budget for each species based on muscle, blood, and liver compartments was constructed and accounted for 75% of the whole-animal lactic acid after activity. The remainder is presumably due to diffusion of lactic acid into other body compartments. It is suggested that differences in whole-animal lactic acid in active anurans can be explained by differences in the involvement of muscle groups during activity, by the fraction of the body mass composed of muscle, and by differences in the accumulation of lactic acid in specific muscles in different species.