The estrogen receptor was extracted in high yield from nuclei of laying hen oviduct with 10 mM pyridoxal-5'-phosphate (PLP). The receptor extracted under these conditions, unlike that extracted with 0.4 M KCl, displayed no tendency to aggregate on sucrose gradients in low salt. The receptor was eluted as a single peak from DEAE-Sephacel at an ionic strength of 0.13 M KCl. The receptor after DEAE chromatography had approximately half the molecular weight of that in the nuclear extract. A larger form could be reconstituted by the addition of whole nuclear extract to the DEAE eluate. These data support the notion that the nuclear estrogen receptor is a dimer composed of similar subunits.