Progesterone receptors: saturation analysis by a solid phase hydroxylapatite adsorption technique.

An assay for cytoplasmic progesterone receptor is described in which receptor is bound to hydroxylapatite and is washed before saturation analysis. Using 3H-progesterone as ligand, the assay yields lower, more reproducible nonspecific binding than is obtained with dextran-coated charcoal techniques and may provide a clinically useful method of measuring progesterone receptor in breast carcinoma. Nuclear progesterone receptors can also be determined by the same technique.