We have previously reported that the platelet count and an increase in platelet number reflect individual erythropoietic capacity in pre-operative autologous blood donation (PABD). We have examined the correlation between erythropoiesis and thrombopoiesis by quantitative in vitro determination of thrombopoietin (TPO), erythropoietin (EPO), and interleukin-6 (IL-6) in patients with PABD. A sequential increase in platelet count with donation could not be explained by an increase in TPO. TPO showed a tendency to be inversely related to the pre-donation platelet count, and to be related to the pre-donation hemoglobin level. There was an inverse relationship between the TPO and EPO levels. As seen with these results, a high erythropoietic state induces restraint of thrombopoiesis, and a low erythropoietic state induces an increase in thrombopoiesis. These effects modulate EPO and TPO via negative feedback. These results provide some practical important information for performing autologous blood donation. Further studies are needed to elucidate the details of these correlations.