Auto-antibodies reactive with brain are known to occur in various immunological disorders. Their significance with respect to disease activity, neurological manifestations, or psychological status is, however, not known. In previous studies it was found that there were antibodies reactive with brain in the sera of patients with rheumatoid arthritis (RA). The present study sought to confirm and extend our previous findings and determine the significance of these antibodies with respect to disease activity. It also investigated a possible connection between psychological function in RA and these auto-antibodies. Sera drawn from 14 RA patients, at bi-weekly intervals over 3 months, showed the presence of antibodies against transmembrane proteins from murine brain. These antibodies correlated positively with rheumatoid factor and joint swelling. There was a trend toward a correlation between depression and daily mood scores and the number of antibodies reactive with brain. In addition, a correlation between cognitive coping styles in RA patients and auto-antibodies was found. There was also evidence for a sub-population of pathogenic antibodies.