Whole Body Hyperthermia (WBH) has been shown to have physiological effects on myeloid and megakaryocytic haematopoietic tissue via both cytokine induction, as well as hormonal changes. In order to extend this knowledge base to the erythroid cells, endogenous erythropoietin (EPO) levels were studied in 17 cancer patients receiving 41.8 degrees C WBH and/or chemotherapy, as well as in 53 anaemic and non-anaemic control patients. Pre-treatment EPO levels showed a 'blunted' EPO response in cancer patients compared to the control patients. Post-treatment data demonstrated a significant chemotherapy induced increase in EPO levels with a peak at 36 to 48 hours (independent of changes in haemoglobin) and 10 to 13 days post chemotherapy (simultaneously with a drop in haemoglobin levels). The early change in EPO levels was not influenced by the addition of 41.8 degrees C (x 60 min) WBH to the same chemotherapy regimen, i.e., ifosfamide, carboplatin, and etoposide. Taken collectively, our data show that endogenous EPO levels in cancer patients can be effected by chemotherapy (independent of changes in haemoglobin). This EPO response to chemotherapy is not impacted on by 41.8 degrees C WBH. A relevant secondary conclusion can also be derived from this investigation, i.e., caution should be exercised as to the use of EPO levels during chemotherapy as predictors of exogenous EPO efficacy.