This review describes recent developments in the chemistry of both fir
st and second generation 99m-technetium-based imaging agents. The mate
rial is presented according to the biological target for the agent, an
d where possible actual images are presented to indicate the type of i
nformation available to the clinician, Beta emitting isotopes of rheni
um offer a possible method for the in situ treatment of cancerous tiss
ue using analogous targeting strategies to those for technetium. Recen
t developments in the relevant coordination chemistry of rhenium and t
heir extension to in vitro and in vivo studies are presented.