In this study levels of serum angiotensin converting enzyme (SACE) were evaluated using colorimetric method in 24 children with congenital hypothyroidism, 28 children from an iodine deficient zone (14 euthyroid, 14 subclinically hypothyroid) and 21 normal children. In the children with congenital hypothyroidism SACE levels (28.15 +/- 6.67 nmol/ml/min) were significantly lower (p < 0.05) than SACE levels in normal children (33.87 +/- 7.00 nmol/ml/min) and in children from an iodine deficient zone (subclinical hypothyroid: 36.05 +/- 7.88 nmol/ml/min or euthyroid: 39.61 +/- 6.83 nmol/ml/min). No statistical difference in SACE levels was revealed in either normal subjects or children from an iodine deficient zone. SACE levels among all the groups were not shown to be different in relation to sex. Average TSH levels, as expected, were significantly higher (p < 0.05) in children with congenital hypothyroidism. The correlation between SACE and TSH levels did not demonstrate a statistical significance in any of the groups studied. In conclusion, our data demonstrated that levels of SACE were significantly reduced in children with congenital hypothyroidism.