A conjugate compound has the structure (I), wherein R.sup.1 is --(CH.sub.2).sub.p --R.sup.6 --(CH.sub.2).sub.q -- where p and q are the same or different and are 0, 1 or 2, and --R.sup.6 -- is --(CH.sub.2).sub.n --, where n is 0 or 1, --NH--, --O--, --S-- or (II), R.sup.1 optionally being alkyl substituted, provided that neither p nor q is 0 unless R.sup.6 is --CH.sub.2 --; R.sup.2 are --CH.sub.2 CH.sub.2 -- or --CH.sub.2 CH.sub.2 CH.sub.2 --, optionally alkyl, alkoxyalkyl or hydroxyalkyl substituted; R.sup.3 are the same or different and are --H, alkyl, hydroxyalkyl, alkoxyalkyl, carboxyalkyl, carboxyalkyl ester, phosphate, sulphonate or phosphonate; R.sup.4 is one of the compounds of formula (III) optionally alkyl substituted, wherein R.sup.7 is --H, alkyl, hydroxyalkyl, or alkoxyalkyl provided that when R.sup.4 is (III d), R.sup.3 is not carboxyalkyl, R.sup.5 is a linker, and Ab is an antibody. The conjugate compound provides for complexes of metals such as Tc, Co, Re, Cu, Au and Ag which are useful reagents for in vivo imaging and therapy.