Indices have been studied for cell-bound immunity in those children with freshly detected type 1 diabetes mellitus (Type 1 DM) who ranged from 8 to 15 years old prior to the onset of insulinization and during its time-related course at month 3, 6, 12, 18 and 24. The control group was 25 essentially healthy children the same age as diabetic children. Prior to insulinization the children demonstrated a significant decrease in the content of T-lymphocytes (CD 3+ cells), with the T-supressors/killers (CD 8+ cells) counts being not different from values in the control group. Relative and absolute number of natural cells-killers (CD 56+ cells) in the blood of children with Type I DM first diagnosed was lower than in healthy subjects. In the time-related course of insulin therapy the CD 3+ cells count had come to be lower than prior to the onset of insulinization. Similar changes were recordable in CD 4+ cells. The content of CD 8+, CD 20+ cells over the period of examination was within the normal range.