By immunoperoxidase labelling of RA (n = 9) and OA (n = 8) synovial sections, we found that CXCL12 was abundantly present on the luminal side of RA sublining vessels (nine of nine tissues) in contrast to OA vessels, in which it was only rarely (three of eight tissues) and weakly detected (Figure 1). The gene discussed is CXCL12; the disease is rheumatoid arthritis.