Significant losses of functional proteins such as hormones and hormone-binding proteins are seen in patients suffering from proteinuria. Studies have reported loss of thyroid hormones and thyroxine-binding globulin in the urine. There is evidence that subclinical hypothyroidism is six times more common in patients with proteinuria than in healthy people. The parameters of the effect of proteinuria on thyroid function have not been fully studiedyet.We investigated 74 patients with qualitatively established proteinuria, of whom 34 men and 40 women, without diagnosed thyroid disease. The average age of the patients was 60.9 years. We tested 20 free controls for free thyroxine (FT4), thyroid stimulating hormone (TSH), creatinine and albumin in serum, and the quantity of urine protein. The mean results found for TSH were higher in the patients with proteinuria than in those of the controls (2.719 mU/l vs 1.78 mU/l). For FT4, the mean result in the patients with proteinuria was 17.04 pmol/l vs 16.39 pmol/l. in the controls. A correlation was sought between TSH and FT4 levels and all the laboratory parameters we tested. Patients with proteinuria had higher TSH levels, probably due to the loss of thyroid hormones in the urine. However, these losses cannot lead to clinically proven hypothyroidism.