The relationship between the timing of maternal tetanus toxoid immunization and the presence of protective antitoxin in placental cord blood was investigated among women admitted to the obstetrical service of the University Hospital in Kuala Lumpur, Malaysia. The 1st dose was given between 13-39 weeks of gestation, with a median of 29 weeks. The 2nd dose was given an average of 4 weeks later. Protection was conferred on 80% or more of newborns whose mothers received their 1st tetanus toxoid injection 60 days or more before delivery. Protective levels were seen in all cord blood samples from infants whose mothers had received their 1st injection 90 days before delivery. Similarly,protective titers were found in 100% of cord blood samples when the 2nd maternal injection was give 60 days or more before delivery. There was no significant degree of protection when immunization was carried out less than 20 days before delivery. A single-dose schedule provided no protection when less than 70 days before delivery. Cord and maternal antiotoxin titers differed by no more than 1 2-fold dilution for almost all of the individual paired sera. A cord: maternal antitoxin ratio of 2 was more likely to occur with increasing time between the 2nd injection and delivery. Overall, these findings indicate that the 1st injection of a 2-dose maternal tetanus toxoid schedule should be given at least 60 days and preferably 90 days before delivery.