Abstract: A conjugate comprises a linear or cyclic synthetic peptide of 3-50 amino acids linked via one of its carboxyl groups and optionally via a linking group, to a polydentate metal chelating group, with the result that endo- or exo-peptidase metabolism of the peptide is substantially inhibited, with the provisos that: a) the peptide chain contains a biological targeting sequence which is biologically active; b) when the spacer is absent the metal chelating group does not comprise solely peptide moieties; c) the metal chelating group does not contain thiol donors. A complex of the conjugate with a metal atom chelated by the metal chelating group is useful in medicine.

Abstract: Novel selenium derivatives of steroids have the formula I, ##STR1## where X is hydrogen or acyl, Y is hydrocarbon and n is 0 or 1, preferably 0. Such compounds, labelled with selenium-75 are of use for investigating body function, particularly for imaging the adrenal glands, and are claimed superior for the purpose to the 6.beta.- and 19- iodine derivatives of cholesterol.

Abstract: Novel selenium-75 derivatives of cholesterol have the formula ##STR1## (I) where X is hydrogen or acyl, Y is alkyl and n is 0 or 1. They are useful for visualizing the adrenal glands of mammals.

Abstract: Novel dimeric and monomeric selenium-75 derivatives of steroids are made by reacting a keto steroid with selenium-75 dioxide or selenious acid-Se75. The resulting diselenide dimers can be converted into monomeric compounds by the use of a cleaving reagent followed by an alkylating agent. The compounds are useful in saturation analyses such as radioimmunoassays.