An assay for erythropoietin in vitro at the milliunit level.

A method is described for the assay of erythropoietin using primary cultures of adult rat bone marrow cells. Either total labeled iron uptake by the cells or hematin synthesis from labeled iron may be used as the measure of erythropoietin action. The method is useful in the range 0.001 to 0.010 U, where the log response is linear with the log dose, and can be carried out in 2 working days. This method has the disadvantage of detecting asialoerythropoietin which has no activity in vivo.