Environmental exposure of infants to perchlorate, thiocyanate, and nitrate might interfere with thyroid function. U.S. women with higher background perchlorate exposure have higher thyroid-stimulating hormone (TSH) levels and lower thyroxine (T4) levels, but no studies have reported individual measures of thyroid function and these goitrogens in infants. Using data and samples from the Study of Estrogen Activity and Development, which assessed hormone levels of full-term infants during the first 12 months of life, Cao et al. (p. 1332) examined the association between urinary perchlorate, nitrate, and thiocyanate with urinary T4 and TSH in infants and whether that association differed by sex or iodide status. Infants with higher urinary perchlorate, nitrate, or thiocyanate reportedly had higher urinary TSH. Children with higher nitrate and thiocyanate had higher TSH, but higher perchlorate was associated with TSH only in children with low iodide. Unexpectedly, exposure to the three chemicals was generally associated with higher T4. The authors conclude that perchlorate exposure is associated with increased urinary TSH in infants with low urinary iodide. Higher thiocyanate and nitrate exposure were also associated with higher TSH in infants.