Formation of the immune system during the neonatal period was studied in 88 infants aged 3 days-1 month (gestation age 28-41 weeks) with the primary diagnosis of cerebral ischemia. The patients were allocated to 4 groups based on chronological and gestational age at the moment of examination and a reference group. A total of 16 umbilical blood samples were available for analysis. Phenotype of blood lymphocyte was identified by flow cytofluorimetry with differentiation between subpopulations of T and B lymphocytes and detection of membrane receptors of IL-2, 8, and 10. T-cell subpupulation was found to be enriched in CD3+CD4+CD8+ lymphocytes. Content of B1 lymphocytes was equally high in full-term and premature infants. The latter showed enhanced expression of IL-2 receptor, CD122, by the end of the first month of life. Expression of receptors of IL-8 (chemotaxis factor) and IL-10 was high in lymphocytes of children of all groups since the onset of the neonatal period. It is concluded that comprehensive study of membrane cytokine receptors is of interest for better understanding mechanisms underlying maturation of the immune system in children of different age groups.