The serum content of thyroxin (T4) and the duration of Achilles reflex was studied in 23 patients with toxic goiter 1-3 months after subtotal thyroidectomy. Concentration of T4 assessed in the serum revealed 9 euthyroid subjects and 14 patients with hypothyrosis. But as the duration of Achilles tendon reflex was within the norm in all 14 hypothyrosis patients reflexometry technique turned to be inconsistent in distinguishing between hypo- and euthyroidism. However the high prognostic value of this method for differential diagnosis of transient or long-standing forms of the disease was shown. Six months after the surgery hypothyrosis disappeared spontaneously, i.e. turned to be transient, in 5 patients whose Achilles tendon reflex parameters were normal, though in all 9 hypothyrosis patients with the reflex parameters higher than 350 m/s clinical and biochemical signs of thyroid under-activity were detected. The data obtained give evidence in favour of reflexometry to be used for early prognostic assessment of post-operative hypothyrosis.