The influence of young red cells induced by anaemization on physical performance had been studied in rats. The anemic rats with immature red cells, higher levels of ATP, glutamate-oxalacetate transaminase (GOT) and lactate dehydrogenase (LDH) showed an elevated lactate and ammonia concentration at the first week of training. The blood analysis also showed that the rise in 2,3-DPG concentration can be related with the increase of glycolytic activity during exercise in both groups, anemic and non anemics rats.