Accurate, rapid measurement of the fraction of unbound estradiol and progesterone in small volumes of undiluted serum at 37 degrees C by miniature steady-state gel filtration.

A method is described for the accurate, rapid measurement of the unbound fractions of estradiol and of progesterone in small volumes of plasma or serum at 37 degrees C by a miniature method of steady-state gel filtration. There is minimal perturbation of the equilibrium between bound and free hormone and no derived kinetic parameters are required. The method has been used to measure the unbound fraction of progesterone in plasma from women during the second and third trimesters of pregnancy and of estradiol in sera of developing female rats.