The study of the phenotype of immunocompetent dendritic cells of the skin in patients with psoriatic arthritis in the course of treatment with deresinated naphthalan (DRN) has revealed some aspects of the mechanism of therapeutic action of DRN. Use of the complex of monoclonal antibodies allowed the authors to determine membrane markers of various cells belonging to the system of mononuclear phagocytes and participating in development of immunoinflammation in the skin. The active stage of the disease is characterized by a fall in the number of CDIa+ cells. HLA-DR+ cells are more resistant. DRN therapy led to prevalence of CDIa+ cells.