Mouth (PmT), esophageal (PesT), and transdiaphragmatic pressure twitches (PdiT) in response to single supramaximal bilateral phrenic nerve shocks were recorded during relaxation between total lung capacity (TLC) and functional residual capacity (FRC) in five normal volunteers. The PmT versus PesT or PmT versus PdiT relationships, which were linearly correlated (all r greater than 0.76), were not affected by diaphragm fatigue and were reproducible on repeated determinations over a period exceeding 1 yr. The PmT versus lung volume relationship was also linear (all r greater than 0.72) and reproducible, and its changes following diaphragm fatigue reliably reflected the changes in diaphragm contractility. We conclude that PmT is a reliable measure of diaphragm pressure-generating capacity in normal individuals and has the potential of providing similar information in patients.