In a group of mothers who received pethidine intramuscularly during labour, drug concentrations were higher in saliva than in blood and there was a significant correlation (p < 0.001) between saliva and blood concentrations measured between 1 hour and 4 hours 20 minutes after dosage. In newborn babies, the pethidine concentrations detected in pharyngeal aspirates were higher than those in umbilical arterial or umbilical venous blood, but there was no correlation. Pethidine was also detected in the saliva from babies for 48 hours after birth. Furthermore, the appreciably higher levels in breast-fed babies suggest that such babies may receive a dose of pethidine in the milk.