Plasma epinephrine and norepinephrine levels were measured in four cases of short term hypothyroidism which developed after parturition. For comparison, six patients with idiopathic hypothyroidism were included in the study. Hypothyroidism was confirmed by clinical evaluation and tests of thyroid function, viz. serum T3, T4, free T4, and TSH. In all patients with idiopathic hyperthyroidism, epinephrine levels were normal and norepinephrine levels were significantly elevated. In the four patients with short term hypothyroidism, normal levels of epinephrine as well as norepinephrine were observed. Circulating thyroid hormone levels start increasing after 6--9 months in patients with short term hypothyroidism reaching euthyroid levels after 1 yr. The present results indicate that plasma norepinephrine concentrations in hypothyroidism seem to be significantly increased only after a lag period of some 6--9 months.