The st.udy was taken to analyze the laboratory findings of the 161 patients with autoimmune thyroiditis treat,ed at Kyungpook University Hospital from January 1992 to July 1993. They were ail female and mean age was 33 years ranging from 10 to 73 years. Mean radioactive iodine uptake(RAIU) of the thyroid was 30.90k21.80(mean+SD)% at 6 hours and 37.97 +- 23.25% at 24 hours. Mean serum levels of thyroid hormones were 1.41 +- 0.48(ng/ml) of T3, 7.26k3.23(ug/dl) of T4, and 1.11 +- 0.66(ng/dl) of free T4, while mean serum level of TSH was 17,99 +- 30.72(uIU/ml). Mean levels of serum autoantibodies were 24. 43 +- 31.91(U/ml) of antithyroglobulin antibody and 55.32 +- 41.97(U/ml) of antimicrosamal antibody, The correlation between RAIU and serum thyroid hormone levels was significantly negative, but the positive correlation between RAIU and serum TSH was noted. The correlation between thyroid hormones and TSH was significantly negative, but the positive correlation between RAIU and serum TSH was noted. The correlation between thyroid hormones and TSH was significantly negative, while antimicrosomal antibody titer revealed significant,ly positive correlation with TSH. The RAIU and free T4 showect negatively correlated with the increasing age. The initial clinical findings of the patients with autoimmune thyroiditis revealed euthyroidism in 83.2%, hypothyroidism in 14.9%, and hyperthyroidism in 1.9%. The incidence of abnarmally increased serum thyroglobulin, ant,ithyroglobulin antibody, and antimicrosomal antibody were 21.3%, 97.5%, and 87.6%, respectively and these abnormalities were more frequent in the patients with documented clinical thyroid functional disturbances.