From the CH(2)Cl(2) extract of the sponge Hyrtios cf. erecta, collected from Fiji, two new sesterterpenes, 1 and 2, and the known compounds isodehydroluffariellolide (3), homofascaplysin A (4), and fascaplysin (5) were isolated. The structures of 1-5 were established employing 1D and 2D NMR spectroscopy and mass spectrometry. All NMR resonances of fascaplysin (5) have been unambiguously assigned. Evaluation of the biological activity of the extracts and pure compounds toward Plasmodium falciparum, Trypanosoma brucei subsp. rhodesiense, Trypanosoma cruzi, hepatitis A virus (HAV), several other microbial targets, and HIV-1-RT and p56(lck) tyrosine kinase revealed new activities for homofascaplysin (4) and fascaplysin (5), both being potently active in vitro against P. falciparum.