Open-heart surgery in Jehovah's Witnesses. During a 7-year period, 11 adult members of the religious sect Jehovah's Witnesses underwent cardiac surgery with extracorporeal circulation. No homologous blood transfusions were given. Blood-conserving procedures were employed, viz. initial collection of autologous blood, haemofiltration or processing (Cell Saver) of blood collected during extracorporeal circulation and reinfusion of shed mediastinal blood. The total perioperative blood loss averaged 1080 ml (15 ml/kg body weight), equalling 19% of total body blood volume. The mean haemoglobin on discharge from hospital was 11.0 g/100 ml. There was no perioperative mortality. Postoperative pulmonary function was good and there was no serious morbidity. Jehovah's witnesses with serious, surgery-necessitating heart disease can be offered operation comprising recognized blood-conserving procedures. 