Summary.Earlier studies have indicated that plasma from blood donations drawn into half‐strength citrate anticoagulant (0·5 CPD‐A2) may give improved yields of factor VIII:C after fractionation. It has also been shown previously that cellular components from blood donations drawn into 05 CPD‐A2 have satisfactory in‐vitro and in‐vivo properties. The present study examines the clinical use of red cell concentrate (RCC) from 0·5 CPD‐A2 blood donations.Forty‐nine patients who were undergoing elective orthopaedic surgery and who required blood transfusion received 0·5 CPD‐A2 RCC. A transfused control group of 107 patients received standard CPD‐A1 RCC for their transfusion requirements. Patients in the two transfused groups had similar haemoglobin responses to transfusion. All patients experienced a moderate pyrexia following the operation. Both study groups showed similar responses to serum lactate dehydrogenase levels in the 2 weeks following surgery, and in postoperative peripheral blood platelet counts. Serious postoperative complications arose in both groups. In the 0·5 CPD‐A2 group two patients had pulmonary emboli (one fatal) and one patient had a non‐fatal myocardial infarction. Three patients had pulmonary emboli in the CPD‐A1 transfused group.These incidences of major adverse events were within the expected range of these complications in patients who were undergoing major joint replacement surgery and did not differ significantly between the study groups. This study indicates that red cell concentrate prepared in half‐strength citrate anticoagulant is comparable to that prepared in CPD‐A1 for patients