Six patients of the Jehovah's Witness faith underwent open-heart surgery without receiving blood at any time. Marked acute decreases in red blood cell mass and low absolute levels of hematocrit followed exclusive use of crystalloid solutions for priming the extracorporeal apparatus and to replace blood loss postoperatively. Sequential studies of renal, cerebral, cardiac, and hepatic function showed no significant impairment up to one week after surgery. There was one operative fatality. The other five patients were discharged ambulatory and improved. Maintenance of blood volume appeared to be a significant factor in prevention of morbidity and mortality.