Abstract: We measured2 and CO2 in six adult bottlenose dolphins (Tursiops truncatus) during voluntary breaths and maximal (chuff) respiratory efforts. The data were used to estimate the dynamic specific lung compliance (sCL), the O2 consumption rate () and CO2 production rates () during rest. Our results indicate that bottlenose dolphins have the capacity to generate respiratory flow-rates that exceed 130 l Ÿ sec-1 and 30 l Ÿ sec-1 during expiration and inspiration, respectively. The esophageal pressures indicated that expiration is passive during voluntary breaths, but active during maximal efforts while inspiration is active for all breaths. The average sCL of dolphins was 0.31 ± 0.04 cmH2O-1, which is considerably higher than that of humans (0.08 cmH2O-1) and that previously measured in a pilot whale (0.13 cmH2O-1). The average estimated and using our breath-by-breath respirometry system ranged from 0.857 l Ÿ O2 min-1 to 1.185 l Ÿ O2 min-1 and 0.589 l Ÿ CO2 min-1 to 0.851 l Ÿ CO2 min-1, respectively, which is similar to previously published metabolic measurements from the same animals using conventional flow-through respirometry. In addition, our custom-made system allows us to approximate end-tidal gas composition. Our measurements provide novel data for respiratory physiology in cetaceans, which may have significant value for clinical medicine and conservation efforts.