A synth .sup.99m Tc complex which contains the moiety Tc.dbd.NR, Tc--N.dbd.NY or Tc(--N.dbd.NY).sub.2 and an organic ligand which confers biological target-seeking properties on the technetium complex, where R is an aryl group, a substituted or unsubstituted alkyl group or the group --NR.sup.1 R.sup.2 ; Y is an aryl group or a substituted or unsubstituted alkyl group; and R.sup.1 and R.sup.2 are H, aryl groups or substituted or unsubstituted aliphatic or cyclic alkyl groups, and are the same or different provided that both are not hydrogen. Radiopharmaceuticals comprising this complex are also described, together with methods for the preparation of the complex.