The influence of the time interval from rupture of the membranes to delivery on neonatal respiratory adaptation was analysed in a prospective study of all infants born in Göteborg, Sweden in one year. The correlation between the incidence of respiratory disorders and the rupture-delivery interval was analysed in all preterm infants (less than or equal to 36 weeks, n = 240) and in all term infants born by caesarean section (n = 452). A uniform pattern was found for all preterm infants, irrespective of mode of delivery, and for the term infants born by caesarean section. The curve was 'U-shaped' with higher incidence of respiratory diseases in infants born immediately after rupture of the membranes than in those born 3-36 h after membrane rupture. The incidence increased again in infants born greater than 36 h after membrane rupture. The same pattern was found for all kinds of respiratory diseases including idiopathic respiratory distress syndrome. Therefore, there seems to be no advantage in postponing delivery greater than 36 h after rupture of the membranes.