We have studied the immune phenotype in thymus and liver, obtained from 7 fetuses with 19-21 weeks gestational age, using the monoclonal antobodies of Russian and American manufacture in reaction of indirect immunofluorescence. The monoclonal antibodies' panels were different for the assay of thymic or liver lymphocyte subpopulations, including CD3, CD4, CD1, CD8, CD38, CD2, HLA-DR, SIg, Ig A, Ig G, Ig M, K- and λ-chains' markers, respectively. The number of CD3+ cells in fetal liver turned out to be quite variable, while the number of B cells was rather stable. CD3+ lymphoid subset from the studied fetal thymus was found to possess 39,25 +/- 2,25%, CD4+ reaching 47,2 +/- 2,2% and CD2+ equaling 60,9 +/- 3,62%, which data are quite comparable with such ones from similar subsets of fetuses with higher gestational age (27-39 weeks): 33,0 +/- 5,45%, 50,4 +/- 3,33% and 63,1 + /- 6,20%, respectively. Besides, we have registered the signs of IL-2 synthesis (0,6 +/- 0,11 I.U.). We conclude that the immunophenotype of thymus and liver in human fetuses of 19-21 weeks gestational age is able to perform certain immune response.