This Microreview seeks to highlight the molecular diversity present in mari
ne organisms, and illustrate by example some of the challenges encountered
in exploring this resource. Marine natural products exhibit an impressive a
rray of structural motifs, many of which are derived from biosynthetic path
ways that are uniquely marine, Most importantly some marine metabolites pos
sess noteworthy biological activities, activities that have potential appli
cation outside marine ecosystems, such as antibiotics, antiparasitics, anti
cancer agents etc... The isolation, spectroscopic characterisation and assi
gnment of stereostructures to these unusual metabolites is both challenging
and rewarding. Examples featured in this Microreview follow a common theme
in that they are all recent accounts of the isolation of natural products
from Australian marine sponges, carried out in the laboratories of the auth
or. In addition to presenting brief comments on specific structure elucidat
ion strategies, an effort is made to emphasize techniques for solving stere
ochemical issues, as well as to speculate on the biosynthetic origins of so
me of these exotic marine natural products.