Doping through increasing [Hb] increases physical performance in sport. Therefore, no cross-country skiers with [Hb] values above 160 and 175 g/l for women and men, respectively, may start in competitions. Even plasma expanders have been used, possibly for lowering a high [Hb] but this procedure may not increase physical performance. There are methods available for detecting the use of erythropoietin but not reinfusion of erythrocytes to increase [Hb]. To make it more difficult to increase [Hb] by different unethical methods we suggest that the [Hb] in endurance athletes is determined both during the training and the competition season to establish individual [Hb] mean values and range. Since endurance training at altitude does not increase [Hb] after return to sea level, an occasional increased [Hb] is suspicious. In such a case complementary doping tests may be used.