Soybean nuclear extracts were prepared to detect SEF3(soybean embryo factor 3), which is presumed to be a trams-acting factor for the expression of the soybean β-conglycinin α` subunit gene. To increase the specific activity of DNA probe during labeling with [α-^(32)P]dATP, dATP was added to a final concentration of 1.1 mM during the chase reaction. It results in approximately four-fold increase of specific activity of the DNA probe. Effects of several modifications in preparation of soybean nuclear extracts were examined. It was found that glycerol is effective to stabilize SEF3 during the preparation of nuclear extracts and polyethylenimine could be used to increase the specific activity of SEF3 in nuclear extracts.