BACKGROUND: Hypervolemic hemodilution (HHD) seems to be a good alternative to acute normovolemic hemodilution to reduce transfusion requirements because it requires less time and effort. In a prospective study in healthy donors, we studied the effects of HHD on blood loss and mononuclear cell counts of aspirated bone marrow which were transplanted. METHODS: After induction of anesthesia and positioning to prone, donors of the HHD group (n = 25) were administered 7.5 ml/kg of pentastarch and the same amount of Hartmann's solution prior to aspiration, but those of the control group (n = 25) were administered only 2 ml/kg/h of Hartmann's solution. Bone marrow was aspirated at the iliac spine and blood loss was replaced with pentastarch and Hartmann's solution for both groups. Hemoglobins and hematocrits were counted after induction, after hemodilution and the end of aspiration. Hemoglobins and mononuclear cell counts of aspirated bone marrow were also counted. RESULTS: HHD decreased hemoglobin from 13.2 +/- 1.1 g/dl to 10.7 +/- 1.0 g/dl significantly (P < 0.01). Even though hemoglobins of both groups at the end of aspiration were not different (9.3 +/- 2.3 g/dl at control vs 9.5 +/- 1.1 g/dl at HHD), calculated blood loss based on body weight through aspirated bone marrow was less in the HHD group (18.0 +/- 1.8% at control vs 16.3 2.0% at HHD, P < 0.05). There was no difference in counted mononuclear cell counts between the two groups (1.8 +/- 0.7 x 10(7)/ml at control vs 1.8 +/- 0.7 x 10(7)/ml at HHD). CONCLUSIONS: During bone marrow harvesting in healthy donors, HHD reduced blood loss through aspirated bone marrow, but does not affect transplanted bone marrow mononuclear cell counts.