The authors assessed in 18 patients with goitre the urinary excretion of neopterin and the blood level of thyroid hormones. They revealed a significant correlation between urinary neopterin excretion and the thyroxine (T4) and triiodothyronine (T3) blood level. This correlation did not apply in female patients treated with large doses of Carbimazol: these patients had a high neopterin excretion, while the thyroid hormone levels were only slightly elevated. This suggests again that Carbimazol has in addition to an antithyroid effect also an immunomodulating action.