A study was made of the time course of the indices of the cellular and humoral immunity in 202 patients with diffuse toxic goiter (grave and moderately grave forms of the disease) aged 17 to 50 with a period of disease from 6 mos to 25 yrs and in 30 healthy persons of the same age. A decrease in the content of T-lymphocytes in the blood in percentage and absolute quantities, an increase in the content of O-lymphocytes and serum IgM and IgG indicated profound disorders in the immunological status of patients with diffuse toxic goiter. It was mostly observed in the patients with a period of disease up to 10 yrs.