Amniofetography is a valuable tool for the diagnosis of fetal malformations. We have studied the effect of radiopaques dyes, containing large amounts of iodide, on fetal thyroid function. We have performed serial determinations of serum thyrotropin and thyroxine in seven newborn infants submitted to amniofetography. This work demonstrates that amniofetography induces a transient impairment of fetal thyroid function.