Thyroxine-binding globulin (TBG) and free thyroxine (FT4) were studied in 172 apparently healthy women giving birth to malformed children. The malformations were divided into two groups: minor malformations (group A) and major malformations (group B). The blood samples were usually drawn in the first trimester. Group A showed no significant difference in TBG values compared to women with healthy children. Group B showed lower, but not significantly lower values in earlier pregnancy. However, from the 15th-16th week of pregnancy the TBG values were significantly lower. The FT4 values were in the hyperthyroid range in as much as 20 % of the women, compared to the reported rate of 0.2% hyperthyroidism in pregnant women.