A new mycosporine-like amino acid, mycosporine-glutamic acid-glycine (λmax = 330 nm; ε = 43,900) with a proposed name mycosporine-glu-gly and the known compound mycosporine-gly, has been isolated and characterised from the sponge Dysidea herbacea found in the Great Barrier Reef, northern Australia. Their structures were elucidated by spectroscopic methods, chemical analysis and comparison of spectral data with those reported for mycosporine-gly or with compounds structurally related to mycosporine-glu-gly. In addition, two other known mycosporines, usujirene and palythene, have been tentatively characterised from the sponge by chemical analysis. This is the first isolation of this class of pigments from sponges and first unambiguous identification of mycosporines from cyanophytes (blue-green algae), either free living or in symbiotic association.