Geographical region of Katowice is situated in an upland built of carbonate rocks, often with predominance of loss. A randomized trial was carried out in the urban population of this area. 1080 children aged 7-13 were examined. In 505 urine iodine was measured. 17.5% of the examined children had enlarged thyroid glands (Ib, II, III) in palpation, 82.3% did not have goiter (O, Ia). Interviews with patients revealed that 48.8% of the examined children used iodized salt, while 51.2% did not. Mean urine iodine concentration was 70.6 micrograms/l. No correlation between use of iodized salt, urine iodine concentration, and goiter was found. However, prevalence of goiter and low urine concentration suggested deficiency of this microelement in the examined industrial region. Therefore there is need for further investigations and for a profound change of the existing ineffective iodine prophylaxis.