To examine the expression of the apoptosis regulatory protein, Bcl-x(L), in the synovium of patients with rheumatoid arthritis (RA) and osteoarthritis (OA). Immunohistochemistry for Bcl-x(L) was carried out on synovial samples from patients with RA and OA. Reverse transcriptase polymerase chain reaction (RT-PCR) and Western blot analysis were performed to qualitatively examine the expression of Bcl-x(L). Bcl-x(L) expression was detected in the lining, endothelium and inflammatory cells of both RA (n=20) and OA (n=10) samples. However, there was significantly more expression in the lining of RA synovium compared to OA (77 vs 61%, p<0.05). Many of the positive cells in the RA subsynovium were noted to be plasma cells. There was a significant correlation between Bcl-x(L) expression and the number of inflammatory cells in the subsynovium of RA and OA patients (r (s)=0.376, p<0.05, n=30). Age and disease duration did not correlate with Bcl-x(L) expression in rheumatoid patients. Bcl-x(L) may play a role in the extended survival of synoviocytes and inflammatory cells in rheumatoid synovium.