The new compound ianthesine E (1) was isolated from the Great Barrier Reef marine sponge Pseudoceratina sp. along with the known metabolites 11-hydroxyaerothionin (2), aerothionin (3) and 11,19-dideoxyfistularin 3 (4). Structures were determined on the basis of their spectroscopic data. The compounds were tested for inhibition of [(3)H] DPCPX binding to adenosine A(1) receptors in a whole cell binding assay. At 100 microM, aerothionin was the most potent, inhibiting 67% of binding, followed by ianthesine E and 11-hydroxyaerothionin which inhibited 61% of binding, and 11,19-dideoxyfistularin which initiated 51% of binding Ianthesine E (EC(50) 60 microM), aerothionin (EC(50) 42 microM) and 11,19-dideoxyfistularin-3 (EC(50) 2.6 microM) exhibited moderate cytotoxicity against the HeLa cell line.