Lymphocytes were studied using indirect immunofluorescence methods employing monoclonal antibodies to CD-markers CD4, CD8, CD16, CD25, CD95, HLA-I, and HLA-II, from the blood of 14 volunteers (aged 18-24 years) before UV exposure (control), after an exposure of blood in vitro to a dose 1.12 kJ, and after 24 hours of exposure of the medial surface of the elbow joint in vivo (S=200 cm2), to a dose of 1.12 kJ.