The Czech Republic (CR) used to be affected by iodine deficiency. Iodization of table salt was introduced as a prophylactic measure in 1947 using potassium jodide (KI) at 12 paris per million (ppm). This level was increased to 27—42 ppm in 1996 together with a program of systematic supplementation of pregnant women with a daily tablet containing 100 ig KI. The change in the program resulted in a complete correction of iodine deficiency in the adult population since 2000, as assessed by the level ofurinary iodine. The present study concentrated on the most at-risk groups to the effects of iodine deficiency, namely pregnant women and neonates. It evaluated the effects of the changes in the program of correction of iodine deficiency on urinary iodine of mothers and their neonates and on neonatal TSR in the national program of systematic screening for congenital hypothyroidism. Urinary iodine was determined in 50 mother-neonate pairs on the fifth day after delivery in three areas of CR in 1993—1995 and in two of them in 1997 (before and after the changes in the program, respectively). Neonatal TSR was determined in 737 776 newborns screened between 1996 and 2003. In 1993—1995 the median urinary iodine values in the mothers (29—72 igJL) and in the neonates (28—77 tgJL) were almost similar and indicated mild to moderate iodine deficiency. In both groups they slightly increased after the improvement of the iodine program (58—79 igJL) but remained below 100 gJL. The recall rate of neonates under suspicion of congenital hypothyroidism progressively decreased from 0.7 % in 1996 to < 0.1 % in 2000 but the frequency of neonatal TSR above 5 mUJL remained above the cut-off point of 3 % up to 2002. In conclusion, in spite of the fact that the CR has achieved iodine sufficiency in the general population, the status of iodine nutrition of pregnant mothers and neonates remained insufficient without special preventive measures, with possible functional consequences in the thyroid function of the offspring. The study confirms that neonatal thyroid screening is a particularly sensitive monitoring tool for the evaluation of the degree and of the correction of iodine deficiency.

        Key words: iodine deficiency, urinary iodine, pregnancy, neonatal thyroid screening