Six new cytotoxic tetracyclic aromatic alkaloids, cystodytins D [3a], E [3b], F [4a], G [4b], H [5a], and I [5b] have been isolated from the Okinawan marine tunicate Cystodytes dellechiajei and their structures elucidated on the basis of spectroscopic data. © 1991, American Chemical Society. All rights reserved.