Changes in the duration of the Achilles reflex were studied in subclinical disturbances of thyroid function. For this purpose the duration of the Achilles reflex, the levels of T4, T3, iodine protein bound TSH and cholesterol were investigated in children admitted to hospital with the general diagnosis of the "euthyroid goiter". Clinical and laboratory findings revealed subclinical types of the diffuse toxic goiter, hypothyrosis, chronic thyroiditis, endemic goiter, nodular goiter, pubertal struma and sporadic euthyroid goiter. The aim of the study was to define the diagnostic importance of reflexometry in subclinical disorders of thyroid function and to assess the relationships between metabolic derangements and the duration of the Achilles reflex. Changes in the duration were shown to correspond to disorder of thyroid function. In 76% of the cases reflexometry brought about the correct assessment of the patient's thyroid status. A significant conformity of the levels of TSH, T3, T4 to the duration of the Achilles reflex was shown.