Relatives of patients with adult onset rheumatoid arthritis, sharing haplotypes, but not having developed the disease, will be investigated to determine whether they produce rheumatoid factor. In addition, their immune response to Epstein-Barr virus-determined antigens will be studied. Children with selected forms of juvenile arthritis will be typed for the HLA-A,B,C, D/DR antigens to further investigate the association with HLA-DR5,DRw8 and LD-TMo. Families to patients with cutaneous lupus erythematosus will be studied.