The affiliations of Karina de Leeuw, Miek van Leeuwen and Marc Bijl were inadvertently omitted from an article in the October issue (van Rossum AP, Huitema MG, Limburg PC, Stegeman CA, de Leeuw K, Van Leeuwen. MA, Bijl M, Kallenberg CGM. Standardised assessment of membrane proteinase 3 expression. Analysis in ANCA-associated vasculitis and controls. Ann Rheum Dis 2007;66:1350–5). They are all affiliated to the Department of Rheumatology and Clinical Immunology, Groningen University Medial Centre, University of Groningen, The Netherlands.