Lyngbyastatin 2 (1) and norlyngbyastatin 2 (2), new cytotoxic analogues of dolastatin G (3) and nordolastatin G (4), respectively, have been isolated as constituents from a Guamanian variety of the marine cyanobacterium Lyngbya majuscula. Structure elucidation of these cyclic depsipeptides relied on extensive application of 2D NMR techniques. The finding of these new metabolites further supports the proposal that many compounds originally isolated from the sea hare Dolabella auricularia are most likely of cyanobacterial origin.