Placental malaria may limit antibody transfer to the fetus. We compared concentrations of tetanus antibody in paired maternal-cord sera from 224 women living in a malarious area of Papua New Guinea. With heavy placental infection (> 35 parasites per 200 white cells) the average cold tetanus antibody corresponding to a maternal level of 1 IU/mL was 0.18 (95% CI 0.12-0.26); corresponding figures after light (< 35 parasites per 200 white cells) or no infection were 0.23 (0.14-0.34) and 0.82 (0.57-1.21), respectively. About 10% of babies born to mothers with a placenta heavily infected with Plasmodium falciparum may fail to acquire protective levels of tetanus antibody despite adequate maternal antibody.