A total of 187 specimens from 142 subjects with rheumatoid arthritis, systemic lupus erythematosus, other connective tissue diseases, and controls were placed in cell culture. Specimens from 119 of the subjects grew, lasting over 2 yr in several instances. No evidence of virus infection has been found by a variety of sensitive methods, including cell fusion. Other approaches have likewise failed thus far to implicate any virus in the pathogenesis of rheumatoid arthritis.