The high incidence of transient thyroid dysfunction in newborns from our hospital (0.6%), led us to investigate whether povidone perineal prep. during delivery and daily postpartum antisepsis, induced iodine overload in the newborn, and whether breast milk was the vehiccle. In a controlled randomized trial we used either povidone-iodine or clorhexidine in 36 mothers, and we investigated in them and in their newborns iodine levels and thyroid function. Iodine levels in cord blood, maternal urine and newborn urine were significantly higher in povidone treated group (p less than 0.001) up to the 4th postpartum day. These levels were also significantly higher in breast fed than in formula-fed babies within the group of povidone-iodine-treated mothers. Maternal prepartum urine iodine, and thyroid function in mothers and newborns were not significantly different in both groups.