CD44 is a widely expressed cell surface glycoprotein which is involved in many cell-cell and cell-matrix interactions. Expression of soluble CD44 splice variants is strictly regulated and is linked to a high rate of cell division. Serum levels of soluble CD44 variant 5 (sCD44v5) were determined in 14 patients with erosive RA. Patients were divided into two groups. In group 1 cyclosporin A treatment (CYA) was initiated after the first visit. In group 2 preliminary CYA was continued. Controls were performed after 6 months. We found a significant decrease of swollen joint count (SJC) and sCD44v5 in group 1. No effect of CYA was found on c-reactive protein, erythrocyte sedimentation rate and IgM-rheumatoid factor (IgM-RF). In group 2 a significant decrease of CRP was found. Therefore we conclude that measurement of sCD44v5 might be useful in monitoring RA+ patients with CYA.