Sensitivity of 15-day mouse fetal liver cells to erythropoietin (ESF). Its practical application to in vitro methods of ESF bioassay.

Demonstration was made of equal reactivity of 13-, 14- and 15-day mouse fetal livers to graded concentrations of Erythropoietin "in vitro". In consequence, replacement by 15-day fetal liver of 13-day liver, currently used as material in Erythropoietin bioassays "in vitro", is proposed as a technical improvement on the method.