Twelve deposit-feeding species of tropical holothuroid echinoderms (families Holothuriidae and Stichopodidae) were surveyed for the presence of UV-absorbing mycosporine-like amino acids (MAAs) during Austral summer at Hicks Reef, Great Barrier Reef (GBR). An additional species belonging to the Synaptidae was collected in Austral winter from Shrimp Reef, GBR. Tissues of all species contained MAAs, including mycosporine-glycine, shinorine, porphyra-334, mycosporine-2 glycine, palythine, asterina-330 and palythinol. The MAAs in holothuroids occur predominantly in their epidermis, which suggests a photoprotective function, since the highest concentrations of these UVabsorbing compounds would be expected in tissues directly exposed to sunlight. Concentrations of total MAAs in dorsal epidermal tissues ranged from 21.9 nmol mg-' protein (Stichopus variegatus) to 2053 nmol mg-' protein (Pearsonothuria graeffei). Taxonomic, tissue-specific and ecological relationships in the occurrence of MAAs in tropical deposit-feeding holothuroids are discussed.