The status of the immune system was studied in 36 patients with the Itsenko-Cushing disease (10 at the initial stage, 12 in the period of recurrence, 14 during remission) and in 20 healthy persons comparing the corticotropin and hydrocortisone content in the plasma. The level of T lymphocytes was lowered at the initial stage of disease (40.6 +/- 3.4%) as well as during recurrence and remission (37.8 +/- 3.9 and 44.5 +/- 4.6%, respectively) as compared to this level in the healthy persons (60.5 +/- 3.6%). The content of B lymphocytes was lowered in all 3 groups (4.3 +/- 0.8,2.9 +/- 0.5 and 4.8 +/- 0.7%, respectively; in the group of healthy persons, it was 19.2 +/- 3.0%). The phagocytic activity of leukocytes was lowered at the initial stage of disease (39.0 +/- 7.6%) and during recurrence (36.7 +/- 4.5%) as compared to that of the healthy persons (44.6 +/- 1.5%). The hydrocortisone sensitive population of T lymphocytes was decreased 1.5-2 times. An increase in the corticotropin level (148.1 +/- 16.9 and 85.2 +/- 19.7 pg/ml, respectively; in health 47.9 +/- 3.8 pg/ml) and in the hydrocortisone level (142.5 +/- 11.1 and 181.3 +/- 20.5 ng/ml, respectively; in health 79 +/- 23 ng/ml) was marked simultaneously in the patients of these 2 groups. During remission (corticotropin and hydrocortisone normal levels), immunological indicators did not completely return to normal, thus suggesting a stable disorder of the cell immunity.