Subpopulational composition of peripheral blood and bone marrow lymphocytes was studied in 17 children with different forms of immunodeficiency, combined with hematological shifts (agammaglobulinemia--6, mucocutaneous candidiasis--2, selective IgG-deficiency--2, hyper-IgM syndrome--3, cephalo-oculocutaneous telangiectasia (COCT)--2, general, variable immunodeficiency--2 patients; neutropenia was observed in all the patients, lymphopenia--in 13, anemia-in 6 patients. Surface markers were assayed by flow cytofluorometry with monoclonal antibodies OKT3, OKT4, OKT8, OKB7, produced by "Ortho diagnostics". Changes characteristic of certain forms of primary immunodeficiency have been revealed in the subpopulational composition of peripheral blood and bone marrow lymphocytes: decreased helper potential in patients with general variable immunodeficiency, T-lymphocyte deficiency in patients with COCT increased number of phenotype T3 cells and decreased amount of B-cell in agammaglobulinemia patients. Significant heterogeneity has been noted in the parameters of hemogram, myelogram and in the subpopulational composition of peripheral blood and bone marrow lymphocytes in each nosologic form, the group of patients with hyper-IgM syndrome has proved to be most heterogeneic. It has been suggested that the changes in the subpopulational composition of bone marrow lymphocytes may be responsible for primary immunodeficiency and disorders in hemopoiesis.