In the present invention a method for purifying erythropoietin comprising at least one chromatography step using a stationary phase containing hydroxyapatite is reported. The method comprises the following steps i) the erythropoietin in a solution containing Calcium-ions is brought into contact with a stationary phase containing hydroxyapatite equilibrated with a solution containing Calcium-ions and namely under conditions under which the erythropoietin binds to the stationary phase containing hydroxyapatite, ii) a solution is passed over the stationary phase containing hydroxyapatite from i) which contains less Calcium-ions than the previous solution and the erythropoietin is not detached from stationary phase containing hydroxyapatite, and iii) a further solution which contains less than 0.5 mM Calcium-ions is passed over the stationary phase containing hydroxyapatite from ii) whereby the erythropoietin is detached from the stationary phase containing hydroxyapatite.
