The ostomy sites of four premature infants undergoing bowel reanastomosis were lavaged with a 10% solution of povidone iodine to reduce local bacterial contamination and the risk of anastomosis dehiscence. There was a significant decrease in serum thyroxin from 112 (+/- 11) mumol/L to 90 (+/- 33) mumol/L 24 hours following surgery (P less than .05), but no change in serum thyroid stimulating hormone (TSH). The total serum iodine rose from 1.5 (+/- 0.05) mumol/L before surgery to 61.6 (+/- 46.4) mumol/L 24 hours later and urinary iodine excretion was 60 times the preoperative value in the second 24 hours following surgery. Both the hormonal and biochemical indices returned to normal 2 weeks following surgery except for total serum iodine, which remained slightly elevated. Povidone iodine is a safe and effective antiseptic agent. However, as it may cause transient suppression of thyroid function in neonates, thyroid status should be tested in all such infants at approximately 2 weeks following repeated or widespread use.