OBJECTIVE: The!aim of this study was to investigate the influence of caesarean section on early pulmonary function of the neonate by examining the tidal breathing parameters in neonates delivered by caesarean section and comparing them with the parameters of neonates delivered vaginally. METHODS: The subjects included 42 neonates delivered by caesarean section and 30 neonates delivered vaginally. Various pulmonary function parameters were assayed by the tidal breathing method within 1 hr after birth. The parameters included minute ventilation (MV), respiratory rate (RR), tidal volume (VT), inspiratory time (TI), expiratory time (TE), ratio Ti/Te (TI/TE), peak tidal expiratory flow (PTEF), time to PTEF (TPEF), ratio of TPEF and total TE (TPEF/TE), expiratory volume at PTEF (VPEF), ratio of VPEF and total VE (VPEF/VE), and TEF25%, TEF50% and TEF75% remaining (TEF25%, TEF50%, TEF75%). Tidal flow-volume (TFV) curves were also constructed. RESULTS: MV (1.16±0.31 L/min) and VT(4.81±1.05 mL/kg) in neonates delivered by caesarean section were remarkably lower than in those delivered vaginally (1.34±0.33 L/min and 5.55±1.24 mL/kg, respectively; P<0.05). The neonates delivered by caesarean section showed faster PTEF (69.40±21.96 mL/s vs 59.03±15.23 mL/s; P<0.05) and TEF25% (62.17±20.62 mL/s vs 51.52±13.83 mL/s; P< 0.05) compared with those delivered vaginally. TPEF/TE (66.08%±11.51%) and VPEF/VE (62.19%±8.69 %) in neonates delivered by caesarean section were significantly higher than in those delivered vaginally(60.36%±9.70% and 55.75%±7.28%, respectively; P<0.05). No statistical differences were found between the two groups for RR, TT, TE, TI/TE, TEF50% and TEF75%. TFV curves of both groups presented with slender and irregular ellipse in shape and peak value in expiratory flow appeared late . In neonates delivered by caesarean section, the TFV curve was narrower and peak value in expiratory flow was higher than in those delivered vaginally. CONCLUSIONS: VT and MV were lower and restrictive hypoventilation was more severe within 1 hr after birth in neonates delivered by caesarean section compared with those delivered vaginally.