The higher risk of respiratory problem in infants delivered by elective caesarean section in comparison with vaginally born infants may be favoured by lower level of nitric oxide (NO) and carbon monoxide (CO) and higher oxidative stress in infants born by caesarean section. We studied healthy term infants born by vaginal delivery or by elective caesarean section. Nitric oxide, CO, guanosine 3-5 cyclic monophosphate, total hydroperoxide and advanced oxidation protein products (AOPP) were measured at birth and 48-72 h of life. Nitric oxide, CO and cGMP were lower at birth and at 48-72 h of life in infants born by elective caesarean delivery. Total hydroperoxide and AOPP levels were similar in the two groups and increased from birth to 48-72 h of life. In conclusion, nitric oxide and CO concentrations were higher in term infants vaginally born than in infants born by elective caesarean section and decreased from birth to 48-72 h of life. The mode of delivery did not affect the oxidative stress which increases from birth to 48-72 h of life.