The aim of this study was to determine interobserver variation in Doppler assessment of mean left pulmonary arterial flow velocity, and its normal values during the first 24h of life. The interobserver variation was determined by a Bland and Altman analysis of the values of mean velocity measured in 21 newborns by 2 observers. Then, normal values of mean velocity were measured in 15 newborns at 5, 10 and 15 min of life in the delivery room, and in 14 other newborns at 1, 2, 6, 12 and 24h of life in the nursery unit. The interobserver variation was found to be acceptable. Mean velocity had a few variations within the first 24 h, but remained consistently above 20 cm s(-1). In conclusion, mean velocity values below 20 cm(-1) suggest low pulmonary blood flow.