To evaluate the effects of interventions during delivery on the maternal and neonatal C-reactive protein (CRP) we prospectively measured CRP by immunoturbidometry in 238 mother-infant pairs (179 normal vaginal deliveries, 36 cesarean sections and 23 vacuum extractions) at 24 and 72 hours after delivery. We additionally measured CRP in peripheral maternal and neonatal blood immediately after birth in 29 uncomplicated vaginal deliveries. CRP values in the mothers and their offspring were low at birth, but rose significantly during the first day after vaginal delivery. Cesarean section induced a pronounced elevation of maternal CRP, but had no effect on neonatal values. Delivery by vacuum extraction produced a transient elevation of both maternal and neonatal CRP at 24 hours after birth. Neonatal CRP values were not associated with presence or size of superficial birth tissue trauma evaluated simultaneously with blood sampling. Increased CRP release in mothers and their infants after interventions during delivery may be associated with varying degrees of tissue trauma and can complicate assessment of the presence of infection.