THE CONCEPT OF GENE THERAPY: Gene therapy is applicable in diseases involving several genes such as rheumatoid arthritis. Gene transfer is the insertion in vivo of genetic material necessary to produce a molecule with therapeutic action. This strategy is currently in experimental stages; feasibility studies in humans are in the preliminary stage. SEVERAL TARGETS: In experimental models of rheumatoid arthritis, the most widely studied target genes are those which code for inflammation inhibitors such as IL-1 receptor antagonists or anti-inflammatory cytokines (IL-4, IL-10, IL-13). Another interesting target would concern genes coding for molecules inhibiting joint destruction (for example metalloprotease inhibitors). VECTORS: The development of high-performance vectors (both viral and nonviral vectors) will greatly improve the expected benefit/risk potential of gene therapy in general. IN RHEUMATOID ARTHRITIS: The particular problem in rheumatoid arthritis is the choice of the transfection site. An articular site would require multiple injections in the different affected joints. A systemic approach would take into account the general disseminated nature of the disease.