This review covers a part of the current general directions in radiopharmaceutical research and development, being the design of ^99mTc-containing steroids capable of binding and imaging the estrogen receptor, progesterone receptor or androgen receptor.

The non-physiological metal technetium has to be adapted to the biological environmental by means of coordination chemistry. As a d-block transition metal, technetium must be incorporated into small-molecule receptor ligands like steroids by some chelation system, which may involve multiple heteroatom coordination or the formation of stable organometallic species. The review will also address examples of rhenium-containing steroids as non-radioactive models for the radiopharmceutically relevant ^99mTc compounds.