Extraction of ER and PgR with 10 mM molybdate in TEDG buffer greatly facilitated their solubilization and a much higher receptor value was observed. However, since molybdate also affects the hormone receptor binding reaction, the apparent receptor activity assayed with molybdate is different from the actual receptor activity normally assayed without molybdate. A correction factor obtained by assaying cytosol with and without adding molybdate can be used to convert the apparent value into the actual value. The mathematical evaluation involving two separate effects of molybdate on receptors is illustrated.