The recent advances in the knowledge of the psychoneuroimmunological pathogenesis of human neoplasms have demonstrated the existence of feed-back mechanisms operating between interleukins and endocrine secretions, which play an important role in the regulation of the immune responses, including the anticancer immunity. In contrast, few studies only have been performed to investigate the possible relation between endocrine activities and hematopoietic growth factors. The present study was performed to analyze the acute endocrine effects of erythropoietin-alpha (EPO) on the main endocrine secretions. The study was carried out in 10 advanced solid tumor patients. EPO was injected subcutaneously at a dose of 10,000 U, and venous blood samples were collected before and 2, 4 and 6 h after EPO administration. No significant changes in mean serum levels of FSH, LH and TSH were seen in response to EPO. Cortisol and DHEAS concentrations increased after EPO injection, whereas those of PRL decreased, but none of these differences was statistically significant. Finally, mean serum levels of both growth hormone (GH) and somatomedin-C (IGF-1) significantly decreased after EPO administration. This preliminary study shows that EPO may inhibit GH secretion from the pituitary gland and IGF-1 production. Since GH would stimulate EPO release, the results of this study may suggest the existence of feedback mechanism operating between GH secretion and EPO production, with inhibitory effect of EPO on GH secretion, and stimulatory action of GH on EPO production. Therefore, this study would describe the first example of hemato-endocrine feedback mechanisms. Moreover, this study, by showing an inhibitory effect of EPO on IGF-1 secretion, would suggest a possible use of EPO in the medical oncology not only for the treatment of cancer related anemia, but also to counteract tumor growth by blocking IGF-1 production, which has been proven to be a growth factor for several tumor histotypes. Obviously, IGF-1 is not the only tumor growth factor, but it could play a fundamental role in the regulation of production and activity of several other tumor growth factors. In any case, this study describes the only acute endocrine effects of EPO. Therefore, further studies, by evaluating the endocrine effects of a chronic treatment with EPO, will be required to establish which may be its effect on IGF-1 endogenous production, and its consequence on survival time.