[en] In 20 males with Stage 2 hypertensive disease, effects of 2-week-, 2-, and 6-month monotherapy with nadolol given in doses 40 to 160 mg daily were examined on the levels of thyroidal hormones (T₃ and T₄) and thyroid-stimulating hormone by means of radioimmunoassay. At the all stages of the therapy, the mean values of the examined parameters were significantly unchanged. Nadolol was found to cause a decrease in T₃ concentrations at its high baseline values (r=-0.57; p<0.05) and in doses greater than 40 mg daily. With reduced T₃ levels in most cases. An inverse relationship was established between the altered serum T₃ levels and the thyroid-stimulating hormone concentration