 Families in which one sibling has developed a systemic rheumatic disease, rheumatoid arthritis, systemic lupus erythematosus, scleroderma, dermatomyositis, or myositis, and the other has not, are eligible for this study. The siblings may or may not be twins, but must be of the same gender and be within a 5-year age difference. Biological parents, or, in some cases, children, will also be included in the study. Normal, healthy volunteers will serve as control subjects. 