I need to label estradiol-17B, progesterone and cortisol with I125. I have lots of experience iodinating proteins, but not steroids.

any ideas out there?

It sounds to me like you will need the services of a synthetic chemist. You'd need to figure out where you can place your label on each molecule such that it won't interfere with binding and then design a specific synthetic scheme in order to incorporate the label at that position selectively (i.e. some serious chemistry, not like just hitting a protein with a labeling reagent). I would probably check to see if there were any commercially available labeled compounds first.

yeah here's a link for tritiated coritsol, probably easy to find the other compunds at similar commercial sites

Rb