Abstract: The invention relates to a technetium-99m complex of the general formula ##STR1## wherein Z is a sulphur atom or an amino group of the general formula R.sub.17 --N--(R.sub.18).sub.k, in which k is 0 or 1 and R.sub.17 and R.sub.18 have the same meanings as the symbols R.sub.1 -R.sub.16 ;each of the symbols R.sub.1 -R.sub.16 is individually selected from the group consisting of hydrogen, straight or branched, unsubstituted or substituted alkyl having 1-4 carbon atoms, and ACOOH, wherein A is a straight or branched, unsubstituted or substituted alkly group having 0-4 carbon atoms;and R.sub.5 together with R.sub.6 or R.sub.9 together with R.sub.10 additionally may form an oxygen atom;Tc represents technetium-99m;t is 0 or 1; andn is 0 or 1;with the provisos that(a) if R.sub.15, R.sub.16, R.sub.17 and/or R.sub.18 are/is ACOOH, A is a straight or branched, unsubstituted or substituted alkyl group having 1-4 carbon atoms;(b) at least one of the symbols R.sub.1 -R.sub.