<jats:p>Three new imidazole alkaloids, naamidines Eand F and clathridine C, have been isolated from a sponge Leucetta sp., together with the known imidazole alkaloids naamidine A, pyronaamidine, clathridine and kealiiquinone. The predatory nudibranch Notodoris gardineri, which was found feeding on the sponge, contained the known metabolite clathridine. The structures of all compounds were delineated on the basis of one-dimensional and two-dimensional n.m.r. experiments at 300 MHz.