The method here described is based on the property of erythropoietin to remain in water solution in the presence of up to 60% ethanol. More than 90% of inert proteins precipitate in the process and can be eliminated without significant loss of the activity. The addition of sulfuric ether produces the separation of the water phase and of its solutes which can be recovered in the solid material obtained by lyophilization. Using this method a marked erythropoietin activity can be demonstrated in extracts of the plasma from mice with a moderate reduction of the hematocrit.