The authors have evaluated the risk of neonatal infection (NNI) by materno-fetal contamination when a rise in temperature occurs in labour and they have worked out the prophylactic measures that should be taken. This has been the results of a prospective study carried out on 6305 deliveries. Any significant conditions associated with NNI are stained liquor and a low Apgar score at birth. When high temperature develops in labour it is important to deliver the infant as quickly as possible particularly if the labour is a premature one. Prevention carried out by very early diagnosis of amniotic fluid infection in pregnancy and by careful attention to the high risk conditions of: early rupture of the membranes, a high level of vaginal infection particularly with Beta streptococci.