The relationship is shown between a concentration of urinary iodine and serum thyroglobulin in population studies carried out on a general population that was randomly selected from the registry of the General Health Insurance Company (individuals aged 6-98 years, 1751 males, 2420 females). The individuals were divided into subgroups with a urinary iodine concentration of <50, 50-99, 100-199, 200-299 and >/=300 microg/l. The mean and median of thyroglobulin were calculated in these subgroups. Tg concentrations were dependent on gender (males<females), age (thyroglobulin increased with age) and statistically significant negative relationship was observed between thyroglobulin and urinary iodine in individuals with urinary iodine <300 microg/l and the age under 65 years. Upper nonparametric tolerance limits of thyroglobulin in relation to iodine intake were calculated in subgroup of normal individuals (n=1858, thyroglobulin, urinary iodine, thyrotropin and free thyroxine were within the normal reference range). Upper limits were dependent on gender and age. The total value of upper limits is 44 microg/l; for individuals aged 6-17 years it is 39.1 microg/l; 18-65 years = 51.4 microg/l and 66-98 years = 60.6 microg/l. In general, thyroglobulin serum concentrations higher than 40 microg/l should be an indicator for determining urinary iodine.