Erythroid regulatory factors: correlation of detectable titers in vivo and in vitro

Titers of erythroid regulatory factors (ERF), as measured in vivo with a standard erythrocythemic mouse technique, showed a highly significant correlation with those obtained in vitro with a fetal mouse liver cell (FMLC) assay. The results from the assay in vitro were somewhat higher than would be predicted from the assay in vivo. Nevertheless, the FMLC technique has been found to be a valid and useful technique particularly in the study of serum ERF titers.