A new cytotoxic alkaloid, renieramycin G (8), was isolated, along with previously reported metabolites mimosamycin (1), renierol (2), and N-formyl-1,2-dihydrorenierone (3), from the Fijian sponge Xestospongia caycedoi. The structure of renieramycin G was deduced from spectral data. © 1992.