Ten normal marrow donors, two children and eight adults, received 9-22 daily subcutaneous doses (100 units/kg) of recombinant human erythropoietin (rh-Epo) and oral iron prior to marrow harvesting. The two children did not have autologous blood stored prior to marrow harvesting while all eight adults did. Except for a mild skin rash at the sites of injection in three cases and transient headaches in a further three, no side effects were observed. The effects of rh-Epo on preoperative and postoperative hematocrits were evaluated and compared with those of control donors matched for age, sex, weight and blood loss. Initial hematocrits were assigned a value of 100%. The mean percentage increase between the initial hematocrit and the preoperative hematocrit in the rh-Epo group was 16% compared with a decrement of 4% in the control group (p = 0.0001). The mean % decrement between the initial hematocrit and the postoperative hematocrit was 4% for the rh-Epo group and 26% for the control group (p = 0.0003). It was concluded from this study that rh-Epo could be given safely to normal marrow donors with a significant increase in hematocrit occurring in the 2-3 weeks prior to marrow harvesting. This approach should be explored further, especially in children, for whom storage of autologous blood is not routinely performed.