[Triiodothyronine, reverse-triiodothyronine, thyroxine, resin-triiodothyronine-uptake and protein bound jodide in the fluid of thyroid cysts (author's transl)].

T3, rT3, T4, PBI and the saturation of T3-T4-binding proteins in yellow and brown cyst fluids of nontoxic goiters differ from the values in sera. In the brown cyst fluids, resulting from a hemorrhage, T3, rT3, T4, PBI and T3 U are significantly higher than in sera and no correlation could be found with the values in sera. In the yellow cyst fluids T3 and T3 U are significantly higher then in sera, T4 is lower, PBI and rT3 do not differ from the values in sera. Only T3 and rT3 are not correlated. Various reasons for higher concentrations of hormones in the cyst fluid such as destruction of thyroid follicles and lymphvessels, a high protein concentration and direct secretion of hormones and iodoproteins from thyroid tissue in the cyst wall into the cyst fluid are taken into consideration. As these hormones in the cyst fluid may be absorbed, the results are also of clinical value.