Cytotoxicity-directed fractionation of an organic extract of the tunicate Lissoclinum patella afforded a new cyclic octapeptide, patellamide F [1]. The structure and absolute stereochemistry of 1 were established by a combination of spectroscopic and chemical methods. Three known cyclic peptides, patellamide B [2], ulithiacyclamide, and lissoclinamide 3, were also isolated and identified.