It has been suggested that a high prevalence of anticardiolipin antibody and lupus anticoagulant in haemodialysis patients may be a feature of dialysis membrane bioincompatibility. Previously published reports have given a prevalence of approximately 30% for IgG-anticardiolipin and 22-30% for the lupus anticoagulant in a population of haemodialysis patients, with a prevalence of 48% for IgG-anticardiolipin in a subgroup of patients dialysed with cuprophane membranes. The aim of this study was to analyse the prevalence of IgG- and IgM-anticardiolipin antibodies, and also the lupus anticoagulant in a population of haemodialysis patients dialysed exclusively with cuprophane membranes. Forty-two patients on hospital-based haemodialysis were studied. Two patients (4.8%) had IgG-anticardiolipin, and 7 (16.7%) had IgM-anticardiolipin. No patients were positive for both IgG- and IgM-anticardiolipin. All positive results were of ‘low’ or ‘medium’ positive titres. In the patients with positive results for anticardiolipin there were no documented episodes of thrombotic events. In the group studied there were no patients positive for the lupus anticoagulant. We conclude that the presence of anticardiolipin antibodies or lupus anticoagulant is rare in this population of haemodialysis patients and they are not a feature of membrane bioincompatibility.