To investigate the relationship between mouth pressure (Pmo) or tracheal pressure (Ptr) and esophagus pressure (Pes) or transdiaphragmatic pressure.Seventeen patients were involved in the study. Maximal inspiratory pressure (MIP), maximal transdiaphragmatic pressure (Pdi(max)), maximal esophagus pressure (Pes(max)), twitch mouth pressure (TwPmo), twitch transdiaphragmatic pressure (TwPdi) and twitch esophagus pressure (TwPes) were measured before narcotization as a normal procedure for the abdominal operation and twitch tracheal pressure (TwPtr(nar)), twitch esophagus pressure (TwPes(nar)) and twitch transdiaphragmatic pressure (TwPdi(nar)) were dynamically monitored during narcotization.(1) The correlation coefficient (r) values between Pdi(max) and MIP, TwPdi and TwPmo, TwPdi(nar) and TwPtr(nar), Pes(max) and MIP, TwPes and TwPmo, TwPes(nar) and TwPtr(nar) were 0.976 +/- 0.030, 0.816 +/- 0.155, 0.923 +/- 0.446, 0.981 +/- 0.185, 0.829 +/- 0.168 and 0.955 +/- 0.292, respectively. (2) The coefficient variation (CV) of MIP, Pes(max), Pdi(max), TwPmo, TwPes and TwPdi were (14.2 +/- 4.7)%, (15.2 +/- 4.3)%, (15.5 +/- 4.1)%, (30.4 +/- 15.9)%, (10.8 +/- 5.1)% and (9.9 +/- 4.0)%, respectively. The CV of TwPmo was the highest (compare with others, all P 0.05). (3) The r value between the changing values of TwPtr(nar) and TwPdi(nar) or TwPes(nar) during narcotization were 0.839 or 0.894 (P = 0.000, respectively).The measurement of MIP and TwPmo should be repeated and the highest value should be chosen in order to reduce the possibility of underestimating the function of diaphragm, which could be dynamically monitored by TwPtr(nar).