Thyroid function was studied in 27 male workers occupationally exposed to lead. The mean blood lead concentration of the workers was 17.07 mu g/dl [standard deviation (SD) 8.96, range 6-36]. The mean and SD duration of lead exposure was 16.70 and 5.38 (range 1-22) years. The total thyroxine (T4), free thyroxine (FT4), total triiodothyronine (T3), free triiodothyronine (FT3), and thyrotropin [thyroid-stimulating hormone (TSH)] concentrations in serum showed an increase compared with the normal values of the Kayseri population (n = 30). However, these values were in the "normal" range of the Kayseri population and Amerlex Firm. In regression equations, the duration of lead exposure and age had a weak but significant association with T4. (C) 1999 Wiley-Liss, Inc.