Urinary iodide and iodine in drinking water were determined in 318 healthy children aged 0 to 18 yr living in Izmir and environmental rural and urban areas in the western part of Turkey. The method is based on substochiometric isotope dilution analysis. Iodide was precipitated by substoichiometric amounts of AgNO3. Iodide-131 was used as a tracer. Electrophoresis was performed to separate (AgI)-I-131 from excess I-131-. The (AgI)-I-131 zone was cut Off the electrophoresis payer and counted with a NaI(T1) scintillation counter. Count rates were plotted versus added KI concentrations. The unknown iodide amount was found by using these linear plots. Iodide concentration ranges were within 1.8 - 100.45 mu g/L in the analyzed drinking water samples. The mean value was 44.14 +/- 17.33 mu g/L and the median was 58.08 mu g/L. Urinary iodide concentration ranges were 0.22 - 142.22 mu g/L. The median of the distribution was 37.71 mu g/L and the mean was 40.30 +/- 24.05 mu g/L. The results show that the examined area suffers moderate iodine deficiency.