Introduction: Iodine, as well as a series of other elements important for heath, occupies a certain optimal dose range of daily intake. It is therefore important for humans to avoid shortages as well as excessive supply. In the second half of 90ties the previous shortage of iodine has been significantly adjusted. The evolution of changes in the population supply with iodine should be further monitored or their causes explored. Objective: to detect changes in iodine in urine ("ioduria") of children and to look for causes of these changes in the nutritional habits Methods: In 1999, 2000, 2004 and 2005 the authors examined a representative cohort of 1209 children at the age of 6, 10 and 13-17 years, living permanently in the region of Jablonec nad Nisou or Příbram. Ioduria as a reflection of iodine intake was determi-ned by the combustion method on the basis of the Sandell-Koldhoff reaction. Information on possible nutritional sources or iodine (sea fish, milk, salting, eggs, and minerál water) was obtained by questionnaire and guided interview. Results: In the course of 5 years there was significant increase in the mean iodine levels in urine from 140 ± 3.69 to 221 [igfí ± 8.66. In both regions there was a significant increase in the frequency of persons with excessive ioduria (above 300 l-ig/1): it was from 0 to 24% in the Jablonec region and from 0 to 32% in children from the Příbram area. In the latter region there was a significant decrease in the frequency of children in the category of optimal iodinuria (100 to 300 ^ig/l) from 86 % in the year 2000 to 53.5 % in 2005. The prevalence of insufficient iodine intake (up to 50 (ig/1) was in the range of 0.7 to 2%. The changes in this category were not statistically significant. In the tested nutritional changes, which could influence the level of iodine in urine, the authors noticed a significant increase in the consumption of minerál water containing iodine: their consumption increased in the course of 5 years from 12% to 15% in the Jablonec region and from 33% to 49% in the Příbram region. A significant increase of sea fish consumption the day preceding the examination was encountered only in children in the Příbram region. In the course of five years there was also a significant decrease in the number of children exposed to thiocyanates from cigarette smoke (stay in the smoke-polluted environment more than an hour a day). Multifactorial analysis of variance of four main nutritional iodine sources (consumption of milk, sea fish, eggs and salt) revealed that regular drinking of milk most significantly influenced ioduria in children. The children having not drunk milk displayed ioduria of 150 Jig/l, whereas those who drank milk daily had ioduria of 187 [ig/l. The difference was statistically significant at 95% level of significance.

        Key words: urinary iodine, nutrition, children, regions of the Czech Republic