Blood doping improves physical performance in sport. This is the reason why the antidoping authorities subject athletes to blood tests. Plasma volume expanders are prohibited agents used to reduce an artificial increase in hematological values using different illegal practices. The aim of our study was to test whether desmopressin (DDAVP)-induced hemodilution would alter the concentration of hematological parameters used to detect blood doping in sports. This was an intra-subject crossover study. Venous blood samples were obtained from eight physically active males on two occasions. On the first occasion the subjects ingested 1.5 L of mineral water and 4.3 microg/kg of DDAVP. On the second occasion the subjects ingested 1.5 L of mineral water. The samples were analyzed for hematocrit, hemoglobin, reticulocytes, OFF Hr-Score, glucose, albumin, creatinine and total proteins. After treatment with DDAVP we found a significant decrease in the hematocrit, hemoglobin and in the OFF Hr-Score values. We also found a significant decrease in glucose, albumin, creatinine and total proteins concentration; however, in this case, all the values were significantly below the physiological levels. Treatment with DDAVP has a very effective hemodilution effect. We consider that this substance should be included in the WADA's prohibited list.