The extinction coefficient at 280 nm of the solution (pH 7,2-7,4) of thyroglobulin from normal thyroid and nodular euthyroid goiter was measured with the values of 0,6-0,7 to 0,9 ml.mg-1.cm-1. The value of E1%280 as function of the iodoamino acid content depends on the morphological state of the thyroid gland. A simple method for determination of the E1%280 value by measuring of the protein absorption spectrum is proposed.