Magnolia virginiana L. flowers were extracted sequentially with supercritical CO2, supercritical CO2 modified with 5% chloroform, and supercritical CO2 modified with 5% methanol at 40 degrees C and 400 atm. The biologically active neolignans 3,5'-diallyl-2',4-dihydroxybiphenyl (1), 4,4'-diallyl-2,3'-dihydroxybiphenyl ether (2), 5,5'-diallyl-2,2'-dihydroxybiphenyl (3), and 3,5'-diallyl-2'-hydroxy-4-methoxybiphenyl (4) present in these extracts, were quantified by HPLC using photodiode array detection. Compounds 1-4 present in one gram dried flowers were found to be 0.11, 1.16, 1.66, and 0.42%, respectively. This is the first report of the supercritical extraction and quantification of bioactive neolignans from Magnolia virginiana L. flowers.