Thyroid and immune statuses were studied in workers continuously exposed to fluorine. The examinees with euthyroid condition had immune disorders with an allergic tendency (increased number of B-lymphocytes, immunoglobulins A). In workers with subclinical hypothyrosis (tri-iodothyronine reduced in 51%), the immune alterations were more evident, T-lymphocytes count rose, but their functional activity declined, indicating impaired cooperation of immunocytes as a result of imperfect control under low concentrations of tri-iodothyronine.